I started playing Valheim on a three-year-old laptop that had a graphics adapter just barely able to handle Valheim. As I progressed through the game my FPS rate got worse so I bought a new laptop with a graphics adapter equal to the one recommended on the Steam Store page for Valheim.

Fired up the new laptop, logged on to Steam, installed Valheim on the new laptop and picked up where I left off in the game. The old laptop was turned off and disconnected from the internet at the time.

So my Valheim data was backed up to the Steam Cloud ready to be downloaded to a new PC. I believe this is its default setting. I normally don't give a thought to where a Steam game stores its data. And Steam uses such portability as a selling point.

Check with Steam to find out exactly how you can ensure you are connected to your last data backup to the Steam Cloud.