GFN stuck at 3456x2160 on 4K external monitor (official app)

Hey!

I’ve just both a Steam Deck Oled to use the new GFN native app. Works amazingly well on the deck, but I wanted to plug it to my 4K monitor and everytime I try, it doesn’t go above 3456x2160 (it’s not 4K native) so I have two black bars on the side. It does this only for this app (even if I’ve set the app to 4K in the settings), it doesn’t do it for other games.

Any solution? Thanks in advance!