What the above is a generalized hypothetical scenario. Do you have any meaningful concrete scenarios that exemplifies the above?
Yes. Jailbreaking is one great example. (For the uninformed, jailbreaks exploit security vulnerabilities to be able to do what they are able to do).
To start, when unc0ver updated to 5.3.0, it gained support for 12.4.1-12.4.8 on these old devices... thing was, they used an exploit of a vulnerability that was patched in 13.3.1 (time_waste)
When Apple released 12.4.9, it did break the tool... only because the kernel version was incremented (the exploit/vulnerability was still there and worked fine without any modifications). Soon after, Chimera 1.5.0 (utilizing a different exploit of the exact same vulnerability for unrelated reasons) and later on unc0ver 6.0.0 would add support for 12.4.9
When Apple released 12.5.5, it also broke all of those tools... for the exact same reason as 12.4.9, tools would eventually be updated and 12.5.5 became a non-issue very quickly.
Mind you, if anyone wanted to, the exploits utilized in these jailbreaks could very easily be used for malicious intent if somebody desired to go that route.
I have apps that still run on my 5s. I have only one app from the above list, Gmail. Out of the millions of apps on both app stores hard to make a generalization. I get that devs don’t want to support multiple versions of their apps with different feature sets. But imo many newer apps that support o/s specific features won’t have backwards compatibility on both platforms.
That's a fair point - the extent people can be affected by app compatibility being dropped can vary wildly for many people, ranging from not being an issue to being a massive issue. And yes, if an app wants to use brand new functionality, it likely has to either implement a pathway for the older OS to ignore the functionality or drop the old OS entirely.
That being said, regarding the devices actually being dropped it does in effect start a time bomb that will keep ticking down with regards to app support, both on an app support scale and on a (where applicable) server support scale
(And for the people who just browse the web, website support can start to degrade over time as well, as can be seen by the various examples of the modern web breaking on older browsers).