So it turns out that BioShock (the original 360 version, not the remaster) has an option in the menus to unlock the framerate! On the Xbox 360 all this got you was ~40 fps and and crazy screen tearing, but on Series X it’s solid 60 fps with no tearing. It’s not an enhanced game so there’s no improvement to resolution, but still pretty cool.
I don’t know why they thought it was a good idea to let you unlock the framerate on 360 hardware… but it turned out to be pretty forward-thinking!