Linux

And can you not see how that's a problem? Software that was written without using XDG portals shouldn't have to be concerned about their existence. If it is required that existing, finished software has to adapt to a new paradigm, it is not a replacement - it's new. And it's intrusive. If you replace the water system for a house, that's one thing. If you replace the water system in the house AND the new system requires the owner to buy and install all new fixtures on all the faucets, that's an entirely different thing altogether.