If you're playing solo you may be able to switch to an older save.

To back up your Valheim save data, navigate to your game's file location. Generally, you can find your save data in the following location:

C:\Users\Username\AppData\LocalLow\IronGate\Valheim\

The Worlds and Characters folders contain your save data. In the worlds folder there will be .old files in there and .fwl and .db files. Once you've backed up everything you can re-name the .fwl and .db files by adding .new to them, then remove .old from the others. Load the game and see if your stuff is back. If not, revert to the originals. You may want to disable cloud saves before you do this.