I put a marker on my map, share the map and tick the ‘include marker’ box, but when I download the map the marker disappears. Ca someone please tell me what I’m doing wrong?
The marker link is meant to be used with a URL, not a downloaded map. This is a link to Wareham Town Museum : https://www.openstreetmap.org/?mlat=50.68615&mlon=-2.10950#map=17/50.68615/-2.10950)).
To save the link you need to copy from the text box in the little menu on the right-hand side of the screen.
The main OSM website is not really geared up for the sort of thing one might expect from Google (it is run by volunteers with day jobs), but there are other tools associated with OSM which might also be suited to what you want to do. At the extreme end there are a couple of sites created by individuals for their local communities, such as that for Bexhill-on-Sea: https://bexhill-osm.org.uk/#14/50.8470/0.4675.
Jerry aka SK53