I understand that Apple did not make enough money to make it worth their while to continue the iphone mini line. However, it does seem like there is a profitable business for someone there given how beloved it was/is.
I only traded out my iphone 12 mini just recently for an iphone 16 pro (likely the last apple product I will ever buy but thats another story) and aside from the camera it is basically the same. Just heavier, awkward to hold and slightly worse designed.
No major player wants a smaller screen because it has downstream impacts on the pipeline of addictive material and ad pixels they can stuff into ocular nerves.
Then few months later they launched the mini expecting it to sell even more or something. Somehow they missed that everyone that wanted a small phone had just bought the SE, and it just wasn't long enough for them to be worth upgrading to the much better mini.
Had they waited for a year to pass the mini might have done much better because those who wanted a more powerful phone could find an excuse for an upgrade after a year, less then 6 months, not so much.
Regardless, battery life is horrendous now, and it's starting to lag and fail so when the new ultra watch is released I'm going to replace my phone with it.
With 3rd party batteries it can't do this, so it doesn't (I think, will admit I'm not entirely sure exactly how iOS deals with 3rd party batteries it can't determine the status of), and if you replaced it with an official part then it would have been in good condition, so regardless which road you took, it's possible that you went from a state where the OS was clocking down, to one where it wasn't anymore.
I currently have this problem (iPhone 11). It's not slight at all. Keyboard inputs sometimes has up to a full 1000ms latency and that's with autocorrect, suggestions, and spellcheck turned off. Scrolling in most apps are jumpy rather than smooth. When this phone dies, I don't know what I'll get. Hopefully a good linux phone exists by then.