Depending on gpu, vulcan can run faster (the stuff game asks you about at launch).
8 fps suggests a laptop and/or dedicated graphics. Valheims low res textures are a visual design choice, not an actual "low graphics". The game takes proper GPU to run all the lightning, terrain and other effects.

Do you pass minimum requirements? If yes it'd try reinstalling GPU drivers and making sure there are no hungry apps running in the background.