I know not every game has a mobile port, and this the way it works for some other media too buying a physical copy of a book doesn't entitle you to an ebook version and vice versa. On the other hand, a steam game can be played on Windows, MacOS, or Linux without restriction provided it's ported or works with Proton.
In any event it still rubs me the wrong way to know I bought Slay the Spire on Steam, and Steam has a mobile presence, and StS has a mobile port, but that still doesn't end with me playing StS on mobile without buying it again.
Hopefully the recent court stuff with Epic and Apple will mean Valve could start putting up their own mobile launcher on iOS, as I imagine they wouldn't see just Android as worth the effort.
No, porting to something that only has touch controls is bad. Touch controls should be only be implemented alongside traditional controls
Slay the Spire probably doesn't need any adjustment on that front
^
there are a lot of add-on physical controllers for phones these days that basically turn them into a steam deck
Depends on the game. Anything where pointing and clicking is the main way of interacting with the game it works just fine.
I’ve played the iPad version of FTL way more than the pc version. Lately I’ve been playing Loop Hero, which works fantastic (icons are a bit small but whatever).