I don't think a Pi 4 would be fast enough to provide a enjoyable experience.
I just tested OpenMW on a Pinebook Pro (RK3399 SOC, should be slightly faster than a PI 4) and I do get like ~30-40 fps with lowest draw distance in Morrowind. Fallout 3 should be even slower due to far more and more detailed objects.
edit: Rendered at a meager 800x600 px