Ok here goes..I might ask MODS :-)that we assemble and get this pinned as a topic. (incase its incomplete :-) )

So world files are in 3 (at least places)

1) Single Player using January 2023 versions and beyond
C:\Users\***\AppData\LocalLow\IronGate\Valheim\worlds_local

2) Single Player using Steam cloud saves here
https://store.steampowered.com/account/remotestorage

3) now Single Player and Multi Player ALSO apparently save to here:
C:\Program Files (x86)\Steam\userdata\yourSteamIDnumber\892970\remote

Good luck and Skall!