When using touch controls on my iPhone 7 Plus connected to my PC running Fedora 29, any game I launch is unable to see the controller or its inputs. Steam Big Picture, as well as my desktop control perfectly, but no games I've tested recognize the controller, and instead assume I am using the keyboard to control. The on-screen keyboard that can be brought up on the app is not recognized by the games either, but mouse control works.

Host OS: Fedora Linux 29
Steam installed with Flatpak[flathub.org]
Games tested:
Castle Crashers (using default version of Proton)
Murder Miners (native)
Clustertruck (native)
Shooty Skies (native)

UPDATE: Tried Portal 2 on a whim, and it worked perfectly! It even applied a custom control scheme which I assume was based off of the Steam Controller configuration. Seems this bug has to do with the game's support of the Steam Controller. Terraria also applied such a configuration (keyboard emulation mapped to the controls), but I was not able to test it further due to being unable to navigate the menus successfully.