ok i hvent played for a while ..untill three days ago..so i backed up (using the Valheim interface) and heres what i discovered (note i use steam cloud!!)
"C:\Users\"UserName"\AppData\LocalLow\IronGate\Valheim\worlds" has a recent file called steam_autocloud.vdf from yesterday..
EVERYTHING ELSE IS FROMm 2022!!!!
however
"C:\Users\"UserName"\AppData\LocalLow\IronGate\Valheim\worlds_local" has all my manual backups from the valheim interface..
the format is worldname in my case Valheim and a lotta numbers.. example "Valheim_backup_20230310-163052" with.dbf as hidden extension size about 86 Meg
and
"Valheim_backup_20230310-163052.fwl" size 1Kb

from that it appears only the manual backups are working, and in my case the Steam cloud is visible when i follow https://store.steampowered.com/account/remotestorage with recent dates!!
if OP cannot find world file on Steampowered. (as stated) then only manual backups seem to exist !!!!