Interestingly enough, there is an inaccessible desert biome in the game currently.

https://gamewith.net/valheim/article/show/25093

Also, the viking trade network extended as far as Constantinople and the black sea, and there's even records indicating that viking merchants reached as far as Baghdad via a route through modern day Russian to the Caspian Sea. So, it's not like deserts were completely unknown to them.