Admins: add Steam64 IDs, one per line, to .config/unity3d/IronGate/Valheim/adminlist.txt, then restart. Admins can use kick, ban and save in the F5 console after running devcommands. bannedlist.txt and permittedlist.txt (a whitelist) work the same way.
ValheimPlus plan: ValheimPlus is installed automatically. Change its settings in BepInEx/config/valheim_plus.cfg and restart. Every player must install the same ValheimPlus version on their PC. ValheimPlus is PC-only, so crossplay is disabled on this plan.