Hey there,

you can check out the pinned guide here in the bug sub-forum or other threads with a similar issue, to see if an old game save is available and how to restore it.

Most current reports here seem to indicate that crashes happen when the game tries to save to Steam Cloud. Apparently, that can overwhelm your setup, especially if your internet connection isn't the best. A potential fix is currently on the Public Test Branch and will hopefully soon be stable enough to be rolled out onto the Main Branch.

To avoid the Steam Cloud until then, you can move your character and world files to Local in the Valheim menu. Then you can turn Steam Cloud off in the Steam Client, either for Valheim or globally for all your games. After that, you should do regular manual backups of your save files, just to be safe. There's a couple of pinned threads here and in General Discussions that should walk you through Valheim's old and new save system.

Best of luck getting your world back!