I have a PHP app written in PHP5.6, for my own use (not exposed on the internet). Naturally it broke when I upgraded to Debian Buster. Upgrading the code would have taken ages; but it took me just a day or so to work out how to get PHP5.6 working on Buster.
I've retired, because I can, and because I prefer not to work if I don't have to. There's a pretty steep learning curve from PHP5 to PHP8; I don't want to do that learning, if it's no longer necessary for my job, and I'm only using it for a private app.
I've not used PHP8 on anything serious, but my impression is that it's a HUGE improvement on PHP5. It's a lot more coherent, a lot faster, and a lot more secure. A lot of what has been dropped was dropped because it was insecure crap - it had to go sooner or later. In the end it was "better late than never".