When does support stop for a piece of console hardware? Its not as soon as possible, its when that hardware is no longer worth supporting.
When you are the market leader in terms of install-base, with 110million+ units in circulation it makes zero sense to drop support on a dime, because even assuming you can match or exceed uptake-rate on the successor hardware its going to take several years to get even half-way to the start-point!
That Sony was going to maintain PS4 support for a few years post PS5 launch was inevitable, as is the way that support is going to taper off gradually over time.
When MS came out with the "we don't believe in generations" line, it was transparently bogus. Because for that to be the case there would have to no difference between the line-ups of the current and (then) next-gen platforms. Inferring that there would be nothing you could play on Series X that you couldn't play on One was of course immediately proven untrue, and to add further proof of it being an entirely empty and baseless marketing slogan when they announced terminating production of the One X.
Of course MS would immediately pivot to say all they really meant was continuity of function thanks to backwards compatibility, but of course certain console warriors are hell-bent on keeping the original, erroneous, take as the same thing Ryan was saying when he called them on their BS by saying Sony do (obviously) believe in generations.
At no point did Sony say that they were dropping PS4 like yesterday's trash, because noone with half a brain would think that was ever on the cards! It was self-evident what was meant.