Fragmentation, there is so many WM, DE, Distros, package managers. This is the beauty of open source but it is also the plague.

Toxic communities, where people are thrashing you if you don’t understand sometimes the overly complicated wiki and you dare open a thread in one of the forums to seek for help.

Driver support, sometimes installing your OS requires a lot of manual configuration to make everything work ok your machine the way you want it.