Now that I think about it, it feels exactly like it felt when I paid off my first car. The phone even cost nearly as much as that beater cost me in my youth.
The reasons I'll eventually upgrade are:
1. I would like a better camera. iPhone X was before iPhone cameras had good low light performance.
2. The older I get the more I could use a larger screen.
3. It cannot run the latest iOS. There's not much I directly need the latest iOS for. I think there are some passkey things that don't work on mine, but it does have some passkey support, which is mostly good enough currently.
4. I cannot upgrade my Series 4 Apple watch to the latest WatchOS. The latest WatchOS requires iOS 17+. And new watches ship with the latest WatchOS so a phone upgrade will be necessary if I ever want a new watch.
I expect that the next time I get an iPhone its camera will be good enough that "better camera" will never again be a reason for me to update. I think they have reached the point where the cameras are better than any camera I will personally ever need.