When I got the Steam Deck I had to install and set up FNV. Once I did that, F3 would work. I would have assumed they had fixed that since then but maybe not? Worth a try.
Honestly, if you own new Vegas have a look at tale of two wastelands. It ports over all of fallout 3 into the new Vegas engine, and with it brings all the upgrades that the nv engine has, like stability (after installing the 20 or so mods needed), iron sights, and all the increased mod support fnv has.
Ok, what am I doing wrong that Fallout 3 isn’t working? It just crashes on start.
When I got the Steam Deck I had to install and set up FNV. Once I did that, F3 would work. I would have assumed they had fixed that since then but maybe not? Worth a try.
FNV worked OOTB.
They are saying that once Fallout New Vegas was installed FO3 also installed fine
Maybe you find some hints here: https://www.protondb.com/app/22300?device=steamDeck (Fallout 3 user reports for Steam Deck) or https://www.protondb.com/app/22370?device=steamDeck (Fallout 3 Game of the Year Edition user reports for Steam Deck)
Honestly, if you own new Vegas have a look at tale of two wastelands. It ports over all of fallout 3 into the new Vegas engine, and with it brings all the upgrades that the nv engine has, like stability (after installing the 20 or so mods needed), iron sights, and all the increased mod support fnv has.