for Linux the world and player character files are at

/home/<user>/.config/unity3d/IronGate/valheim

the .fwl are under the /worlds directory


and the executables are at

/home/<user>/.steam/debian-installation/steamapps/common/Valheim

just copy /paste the OQ relevant path into explorer location bar or use the file and folders search tool to look for <worldname>.fwl or just *.fwl

Hope this is useful and good luck :)