I think it kicks in when you distribute. For example, let’s say I have a fork of some GPL software and I’m maintaining it for myself. I don’t need to share the changes if I’m the only one using it.
The point is that people using a software should be able to read and modify (and share) the source when they want to.
IANAL and all that good stuff
I have no hdr and other shenanigans but I’ve been using auto login via sddm for my plasma wayland session since a long time and it works.