For examples of cross gen compatibility, the Xbox Series console is compatible with approximately all Xbox One titles, the PS5 is compatible with approximately all PS4 titles, the 3DS was backwards compatible with basically all DS titles.
Really the notable breaks of late have been PS3 to PS4, and WiiU/3DS to Switch.
For examples of continued compatibility within a generation... every console ever? I think there were a handful of PS2 titles that had graphical bugs on the slim PS2? But that's going back over 20 years.
It is infinitely more than the number of iPhone apps that have not recieved updates in 6-8 years that are still runnable. Even mac apps will often have trouble in that kind of time frame.
You're also the one who expected "all" to work cross gen. My original point was just that "all" would work on the software for a given piece of hardware that worked on the original hardware. The fact that 99.9% also work on the next gen is a bonus, because the same gen compatibility already leaves Apple's backwards compatible story in the sand.
Some consoles did ship an emulator for the previous generation, and they don't support all titles.