I should have been a more clear. I flashed Merlin firmware on the new router. Not on my laptop.
Many providers do it... sadly
I have never had one actually require it, often the installers will claim that but back in the day I would just say "sure here is my linux machine have fun installing your windows software on it" and magically they did not need to install anything any more....
But as one can imagine people (99% are on Windows) do it in haste...