I can confirm this worked for me as well. Interesting work around.
I've got an Xbox 360 controller, plugged in via USB.
Started trainer, activated with F1 OUTSIDE of the game
Went back into the game, pressed a controller button. Game immediately recognizes the controller.
Closed ingame menu and used the controller to navigate myself through the world.
It's not the trainer and game is buggy. Try again. Switch to windowless fullscreen in video options and activate trainer while trainer window has the focus. Then go back into the game.
Game switches to keyboard as soon as you press a keyboard key. I think this is the "issue" you guys/girls have.
[Edited by 0x90, 12/10/2020 9:18:34 AM]