The evergreen browser is a thing, but the idea that everyone can
trivially upgrade those browsers is promulgated as true when it's a bit of a myth.
It is sometimes expensive for people to upgrade browsers, called evergreen by developers so they can avoid annoying support expenses for a few percent of people.
I had a phone running a Mozilla browser, which received updates until it didn't any more.
Then the only way to upgrade browser was to purchase a new smartphone.
Unfortunately it was a superb device with no newer replacement, so to upgrade browser I had to downgrade my smartphone for other uses, and pay the cost of an expensive new smartphone despite not really wanting one. But sites saw it as "you are running an old Firefox, you obviously can trivially upgrade".
I still have a perfectly great old Android tablet running an old version of Chrome which cannot be updated. Other than website compatibility, everything on it that it is used for is still working flawlessly. Perfect screen, sound, wifi, memory, battery.
For now, enough sites work on it that I still use it. That can be replaced easily with another tablet, but it is disappointing to have to spend cash and throw away a working product to e-waste, just to replace it with a functionally identical device because of the way the software treadmill works. (It doesn't have to work like that, it's a choice made by developers collectively.)