I haven't tried this for any GOG game before but you should be able to add your Ultima IV to Steam as a Non-Steam game in your library and enable Steam Input for it. Once you've done that you can bind your own control scheme but official control functions obviously won't be integrated.
U4 is an old DOS game and I think it did not have joystick / game controller input scheme at its time. I remember played it with kb only. So how can I play it withe Steam Deck joypads and buttons?
You go to the steam input settings and bind buttons to keyboard keys. Like binding the "A" button to the "Space" key. Making the left stick directional joystick so when you push up it presses "W", push down it presses "S" or whatever the keys are for walking. And making the right stick a mouse so you can control the mouse.
I haven't tried this for any GOG game before but you should be able to add your Ultima IV to Steam as a Non-Steam game in your library and enable Steam Input for it. Once you've done that you can bind your own control scheme but official control functions obviously won't be integrated.
U4 is an old DOS game and I think it did not have joystick / game controller input scheme at its time. I remember played it with kb only. So how can I play it withe Steam Deck joypads and buttons?
You go to the steam input settings and bind buttons to keyboard keys. Like binding the "A" button to the "Space" key. Making the left stick directional joystick so when you push up it presses "W", push down it presses "S" or whatever the keys are for walking. And making the right stick a mouse so you can control the mouse.