Updates:

- Swapping the cross and circle buttons moves the problem to the circle button. suggesting that the problem is triggered by receiving the A Button signal from Steam Input rather than a direct hardware conflict. (Obviously it's more than that, else this would happen with the Steam Deck's controller.)
- It doesn't seem to be a full-on hard crash per se as a closing animation (the short "wipe" effect) plays before the game closes. Interestingly, this "wipe" does *not* play if I select "Quit" with the faux-mouse.
- Some of the options screens work. Once I reached the Video options using the faux-mouse, I was able to switch resolution using only the controller.
- Switching from fullscreen to windowed mode did not solve the crash issue.
- Going to start the game using the faux-mouse, I can select New Game or Import just fine with the controller.

Basically, some UI controls work with the controller and some just explode when pressing whatever is mapped to the A button, and I haven't discerned a pattern yet.

Another interesting tidbit:

With the trackpad still set up for mouse movement, I set clicking the trackpad to the A Button. This made it more difficult to crash, as if the game registered a mouse movement and switched to mouse UI mode, pressing the button did nothing at all. I had to move the stick (switching the game back to controller mode), then carefully click the track pad without dragging my finger on it for it to crash.

This is a fun bug!

Also, at least once the game crashed pressing the B button (mapped to circle), so it's not just the A nutton involved.

This looks complicated, and probably not something I can work around here. Guess I'm SOL playing this on the couch for the moment -_-