A shared way for cyclist and pedestrians can be mapped with: (besides highway=path and highway=footway):
highway=cycleway + foot=designated
or
highway=cycleway + foot=yes
Is the choice between these two only subjective?
If not, what’s the difference?
(I have read the wiki, but still confused)
If a path has offical sings for a combined cycle- and footpath they both have equal rights. In this case use highway=path and foot/bicycle=designated and segregated=yes/no.
If a path has a sign which declares him as a footpath and an aditional sign cyclists allowed it means foot has priority. In this case use highway=footway and bicycle=yes
Same but opposite for path signed as cycleway.
Last of all bicycles and foot are allowed but there is no sign at the pathside us highway=path and foot/bicycle=yes and if you want segregated=yes/no.
As a German, there is:
highway=cycleway is a designated cycleway (i.e. implies bicycle=designated). That means, it’s either signed with a blue sign (primary characteristic) or it’s an unsigned way with painted bicycle symbols (secondary characteristic).[1]foot=yes implies permissive use for pedestrians (serves primarily cyclists but supports pedesrians).[2]foot=designated implies the cycleway is built with pedestrians in mind which translates to a mixed-use resp. segregated foot- and cycleway (equal modes).[3]The unambiguous case. ↩︎
In Germany, this would be represented by a blue cycleway sign with “
frei” which mirrors a designed footway with bicycle permit (blue footway sign with “
frei”. ↩︎
It’s also presumably the reason why highway=path+foot=designated+bicycle=designated is particuarly common in Germany over the other because that tag doesn’t deemphesise pedestrians. ↩︎
You won’t be able to get a general answer to this question, because foot=designated can be interpreted in many ways. Some say, foot=designated requires a blue sign, some say it requires any form of sign, because foot=yes doesn’t mean “pedestrians allowed”, but rather “pedestrians not prohibited”. The only thing that’s sure is: if there is a blue sign, use designated 
To clarify this: that’s not true everywhere. Also, it’s written nowhere that designated has priority over yes (or pedestrians have priority over everyone else of highway=footway), so that would also be country-specific.
As western neighbor, for NL the default is highway=cycleway + sidewalk=[left/right].
The reason is that in NL the pedestrian part has often a different surface and the sign used for these path does not have a pedestrian pictogram.
The original question is a good and understandable one, but it is hard to answer it succinctly, because there is little or no collateral information about what specific type of ‘shared way’ @Msiipola has in mind.
In general, I’d also argue that this very much depends on both whether there are traffic signs present and on what specific country we are talking about. The Nordic style Freedom to Roam laws have a massive effect here too.
In Finland, we are in the middle of renewing our documentation on tagging footways, cycleways and paths. This work was instigated (among other reasons) by new traffic laws that came into effect the first of June 2020 and introduced lots of new traffic signs (and e.g. made all traffic signed cycleways oneway by default, unless there is an additional traffic sign that permits bicycle traffic both ways). Link to the proposal wiki page is here (notice though that that wiki page is written in Finnish, and Google Translate probably botches a lot of the text, especially the legalese).
My question applies to Sweden, where walking is almost allowed everywhere if no signs or default rules says it’s not allowed. In these cases no need for foot=yes or foot=designated.
I also don’t consider a cycleway to be a “path”. But that’s my own subjective opinion. No point discussion it here.
Yeah, in Finland we use highway=cycleway + bicycle=designated + foot=designated for cycleways that have the blue sign with a pictogram of a bicycle and a pedestrian.
The highway=cycleway+ foot=yes combination is a bit more problematic one, and is reserved for some non-traffic signed ways (the ones that are physically suitable for all kinds of bicycles). The Freedom to Roam laws grant near universal access in Finland to walk and bicycle on all non-traffic-signed ways, so here highway=path itself directly implies the foot=yes and bicycle=yes tags. Here, the choice of cycleway vs. path is a slightly difficult and somewhat subjective one. On the other hand, one is not allowed to walk on a cycleway that has a blue sign with only bicycles allowed, and also not allowed to cycle on traffic signed footways. But e.g. in Germany they apparently do have traffic signs for footways where ‘polite’ bicycling is allowed. There was a thread on that signage here not that long ago. So in some countries the cycleway+ foot=yes combo may have that specific meaning.
Sure, a cycleway that has a traffic sign marking it as a cycleway is quite naturally a highway=cycleway and (at least) bicycle=designated in OSM. Like I said, it all depends on what one specifically means by a “[a] shared way for cyclist and pedestrians”, as your original question was.
designated is usually more like a “you have to use it, if you use this way”, yes is more like you can use it. Not sure whether tat makes any difference in your country for pedestrians.
Tanks for the clarifying!
Just to be clear, something like foot=designated doesn’t mean the way is only for pedestrians. The designated value originally had this definition:
The specific meaning varies according to jurisdiction. It may imply extra usage rights for the given mode of transport, or may be just a suggested route.
Over time, mappers and software developers have interpreted this value variously, but “only” is unfortunately a common misconception, especially as it relates to specialized keys like hov=*.
I do not see this making sense. When I use a way, I do so to get somewhere. If I do so voluntarily or by being forced, what does openstreetmap care about it?
In German “Benutzungspflicht”, like you would not be allowed to walk on the road or cycleway
Standing at a crossroads, would a designation a.k.a. “Benutzungspflicht” be able to force me to go somewhere that I do not intend to go? In Austria, definitely no!
Is this accurate? 
Perhaps you meant to say: You have to use this way, if you wanted to use the other way. As far as I know, this better tagged on the other way via “foot=use_separately_mapped_sidewalk” or such.
In OSM one road can consist multiple parallel ways. The one which is designated you have to use if you use that road. Of course you can choose a different road at the intersection.
The question wasn’t about how to tag something but about whats the difference between yes and designated. I don’t disagree with you, that there are different/better ways to tag it.
For sure it is and police will stop you, if you don’t have your light on at night and charge you a couple of Euros. Luckily in Germany they don’t have comparable gun laws than the US 
I think this is called “lane mapping”? I question the usefulness of adding *=designated to one such separately mapped lane to help a consumer figure out which lane to avoid, I see no evidence of that being followed by the three routers available from the main site. I observed mappers adding foot=no to the highway=residential, so routers use the separately mapped sidewalk.
What is truly new to me in this topic and others coming up recently, in the Netherlands, cycleways have sidewalks?
Hi,
True! But no need to invent a new tag for that purpose. Apparently you were completely unaware that the bicycle=use_sidepath and foot=use_sidepath tags exist already and are used precisely for the purpose you mentioned. I’d argue that the existence and use of these tags does not mean that a =designated tag on the other way would be superfluous, though.
E.g. in Finland, the law states that if there is a designated cycleway adjacent to or nearby a highway, bicyclists have to use the cycleway instead of the highway (unless the cycleway is unuseable because of unploughed snow, etc.). So we need the use_sidepath tags too to express this.
Good point by @Minh_Nguyen that designated does not itself mean that other traffic would be forbidden! It just means that the way is “designated”, by whatever means (e.g. by a traffic sign), as a preferred way for some traffic. The =yes access tag denotes the absence of a legal restriction. I think that there is an intelligible, albeit perhaps slight, difference between the two.
Here in the North, our FtR laws mean that the foot/bicycle=yes access tags are mostly superfluous. foot=yes is used in combination with some (Duck Tagged) highway=cycleways precisely to denote that that way does not have a traffic sign that would forbid walking on that way. The =cycleway tag alone would leave that detail ambiguous.