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.
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.
It seemed to be because the pre-launch scripts weren’t executing. Installing the other game ran similar scripts which fixed it somehow.