It is just software. The only thing PureOS does it not ship with the firmware necessary to make those proprietary hardware components work out of the box. It's

It is just software. The only thing PureOS does it not ship with the firmware necessary to make those proprietary hardware components work out of the box. It's essentially Debian but without the non-free repo. Nothing stops you from making PureOS work on hardware with proprietary firmware if you want to. It isn't locked to only work on libre hardware, it's just a bit more tedious.