Recently had some issues with the steam cloud in general and lost a lot of Savegame-files of various games.
Luckily, Valheim wasn't affected.

But because of this I highly recommend making a manual backup of your save as well.
You'll find them in the appdata/local low directory of your system drive.
Zip the entire directory and store it somewhere safe.

If this save had gone too, I'd propably had my PC thrown out of the window.