I think I solved the issue by manually setting up a new APN profile with the settings listed here Mobiloppsett | Telia
I tried sending a setup SMS with the service provided on the page first but it did not seem to have support for the Fairphone 6 which provably explains why it doesn’t work properly out of the box(?).
I have no idea why using a Wireguard VPN seems to solve the issue. I might try to contact telia about this at some point as this phone is mainstream enough to be sold at elkjøp but the thought of explaining Fairphone, e/os and Wireguard to a level 1 tech support is daunting 