RPG Maker games are playable on Steam Deck.
First of all, you probably need to edit keybindings to adjust to your liking.
You can accidentally turn off the fullscreen mode (or it turns off by default - I'm not sure why). You can switch keybindings for a moment to fix it.
You can use the touchscreen without the Touch UI setting, however you won't be able to return from conversations / choice menu.
tl;dr
Friend claims: games are playable, but you need to figure out the keybindings yourself and properly adjust them.