Thanks for helping @RichardBray, I also think Gama11 could help as they already solved so many of my problems, but I know they don't hold all of the answers.

For the record, both Gama and Ian (haxeui) already checked out my problem and kindly tried to help me, unfortunately all attempts have failed so far.

Gama11 suggested I swap lix for https://github.com/krdlab/setup-haxe in my .yml in order to check if it was a lix bug.
I tried doing that but then discovered that lix is required in order to setup flixel, so I got back to square 0 without gaining much unfortunately.

Ian suggested I swap haxelib git haxeui-core https://github.com/haxeui/haxeui-core with git clone https://github.com/haxeui/haxeui-core and haxelib dev haxeui-core haxeui-core, so I did that and unfortunately nothing changed.

Very baffling stuff