Is there truly no gamepad support for this game? No matter what I do in the settings, no button presses are registered when I try to change the controls. I'm using an 8Bitdo SN30 Pro + controller.

Have you switched input method to controller? If it still doesn't detect you inputs try the detect gamepad option.

For me to get it to work, after switching input to controller, I had to change my Port from 0 to 1, and then you have to do manually map the controls to each button (using a mouse/pad pad to select the action, and then pressing the button on the controller).