I'm seeing a lot of posts about people having issues after the latest update. Granted the fix is easy for most (i.e update your mods)– but here's a solution I've been using since I used to run a 7 days to die server (a game that's been in "early access" forever with lots of updates) for my friends:
Make a copy of the game in your steam directory, rename the folder and use if for playing/modding.
Steam will update the vanilla version and leave your modded one untouched. I do this so that I don't have to worry about an update breaking anything or a friend having trouble getting his game version/mods updated.
The server and our client files then remained "locked" to the version we made a copy of.
An important note– you'll only be able to play with people/servers on the same game version as you, and you still need steam running to open the copied folder.
Every once in a while when an update is substantial enough I start the process over with the newest version!
Source: https://www.reddit.com/r/valheim/comments/vgyyws/if_you_dont_mind_missing_updates/
