While not ideal, advising to go to the forum isn’t technically wrong, there’s lots of information here (such as one of my old posts about the marker: Folder markers are now directories (v0.14.38) - #52 by Nummer378)
When I search for “folder marker missing” on the forums most of the information is good. The very first Google result appears to be an old thread from 2015, which indeed advises at some point to just recreate the marker. It does contain a warning about potential data loss just a reply above, though.
Yes, one has to properly do some research first instead of typing in the very first thing that catches the eye. This could be alleviated with a direct link from the error message.
In the docs we indeed don’t really make the dangers fully clear. We only mention it in two places (here and here)
Indeed, we should probably add a proper FAQ/entry in the docs regarding the specific error message “folder marker missing” that explains the various situations causing it plus the consequences of recreating it and then link to that. This has been brought up some time ago, though it apparently never happened, probably because no one wrote the PRs.
This is what happens when you remove and readd the folder from within syncthing, which is basically why the error message advises to search the forum, since it’s been mentioned here a few times.