Originally posted by Qbertos:

Instead of on the shortcut link, do the '-window-mode exclusive' via the Steam Library - go and find Valheim and right click and under Properties find Launch options and enter '-window-mode exclusive' there and it should work much better for you.

Also, if in game, just do an Alt-Enter and back again if you want to confirm your fps is where you expected it to be or if you want to double check. Hope this fixes your issue!

Thanks for that reply, but I also tried that and same issue.

The issue persists and I am wondering why.