3.1 can do mode promotion on an AGA machine when you have the DBLPAL monitor enabled. You don't need to have a DBLPAL screenmode selected, it's enough to have mode promotion on and DBLPAL loaded.
https://commodore.bombjack.org/amiga..._Workbench.pdf
Pages 110, 145 onwards, specifically 160
Depending on how the game you're running opens its screen, the OS may promote it.
You never mentioned whether you're running these with WHDLoad or not.