I’m nothing to do with the administration of the site and certainly not part of the forums governance team, but based on what has been said previously:
A “thumbs down” reaction has been widely discussed as being essential before the Help site is migrated from OSQA to here.
The help site isn’t going anywhere until the old forum has been migrated from FluxBB to here (there are numerous discussions on the progress with that elsewhere).
The admins have been quite busy recently dealing with issues caused by the upgrade to Discourse 3.0
There’s actually a “solution” to this question here, but essentially that says “we’ll look at this when move on to supporting help.osm.org functionality”, which seems like a sensible approach to me.
That is surely the only sensible solution to the problem of sorting replies to help and support questions by up and down votes.
Being able to provide a “thumbs down” reaction is a slightly broader topic, as it is about being able to provide a reaction to any post, not just downvote a support reply. Being able to downvote a support reply is obviously necessary if we want to sort by the algebraic sum of +1 () and -1 () votes.
Hopefully admins will find time for looking into this once solved the mentioned upgrade.