@loftcat
About Symbian version, first attempt was in Symbian WRT (HTML, JS), shortly updated with QT Quick (QML, JS, C++ inline for OS things like minimize/resume), with addition of Inneractive network for in-app ads. Generally I had positive feelings specially from QML, but it was little to late in Nokia Store life cycle, soon Nokia switched to Windows Phone (that also wasn't bad OS).
Main reason to prioritize Steam version is that it gives chance to make any $ - wider audience, users that are willing to pay for games, and it's main platform for PC games, itch.io is good for contests, and small original concepts that are not final games - to raise interest.
Steam/itch itself doesn't imposes way of coding or something, both tool sets are easy to use for updating game builds and so on. Most important that docs are easily available so you can check how steamworks build process works :-)
@spacefractal
Huge thanks for testing game with real Steam Deck

Good to hear that it's working properly without serious issues, for music I'm using
this SDL2 code.
That level UI selection issue in Twisted Line, yeap - good hint, will need to look into other similar 'selection' inconveniences, so playing with gamepad will feel better. Thing with selecting only last/recent end of line most likely was designed to simplify writing 'undo move' function, and you are right, both ends should be 'selectable', that also will be fixed, need some testing if fast/easy fix will be sufficient or requires something more. I will look into help screens, maybe create some additional, specially as you can cross lines with different colors.