Ideally 1.20.1, since it's the most widely-used version.

What about main modded version?
When it will come out?

Updating to 1.21

Define "main modded version", there is no one main modded version, currently 1.21.1 is the current modding target since all modders aim for that version rather then going for .2, .3, .4 etc etc, so for now our main loader is Neoforge and target version is 1.21.1