If you want to know how that works you can read up on Git branches here: https://git-scm.com/book/en/v2/Git-Branching-Branches-in-a-Nutshell
Realistically, if you know nothing about Git or app development, you might just be better off participating in their issue tracker and their pull requests page. E.g. here is a discussion about Wine support dating back to 2016. Maybe tell the developer there that you're interested in helping and they might point you in the right direction.
Thank you, I keep wishing more people would do a deep dive and report back. Here are my reviews ( only one game in common!)
XCOM:EW or XCOM 2 are the big budget games with the "same"(actually much more in depth) concept (and the long war / long war 2 mods especially - there's probably been more manyears spent on just balancing those mods than on making Depths of Extinction, though hilariously enough some QoL features are much better in DoE). XCOM:EW can be had for really cheap these days when it's on sale (it's on android too: https://play.google.com/store/apps/details?id=com.tt2kgames.xcomew).