I'm pretty much in the same boat, all my smartphones have been Android phones and I was always excited to see what changed from version to version because Google had a good track record. I didn't agree with every change but for me, the change from Android 11 to 12 was unbelievably mindboggling, and a complete change of pace from everything before. And worst of all, you could not disable everything I list:

- Everything suddenly had to be a large round button which took up more space than necessary. The notifications + quick options menu in particular became suddenly bloated. In particular the keyboard press preview when from neat little rectangles to large distracting circles to the point where I had to turn it off.

- A ton of transparent elements were removed with a simple black box, which removed a sense of continuity when using my phone. Dragging down my notifications didn't show me the app in the background, and switching between apps didn't show my wallpaper in the background. It might seem minor, but it's such an odd change to make after so long and I struggle to see why Google decided to remove the ability to see everything behind the notifications menu.

- Android 12's UI colour schemes were suddenly dictated by your phone's wallpaper, but the palettes are a selection of garish pastel colours. Until Android 13 toned it back a bit I was reliant on using a monochrome wallpaper to have the notifications menu (now a screen-filling behemoth) not be a selection of greens.

- Google introduced a stretchy rubber effect when scrolling through everything which to me was suddenly jarring (especially when it'd break at the bottom of a page or while holding my finger in place). I clearly remember it being the first thing I tried to disable, but the only option that seemed to stop it was to remove animations as a whole.

- Google removed the old split screen feature and replaced it with a less functional "app pairs" system. Before Android 12 you could pin any app to the top half of your screen and switch around other apps on the bottom half, a great feature if you wanted to multitask or simply wanted to watch a YouTube video while jumping between browsing the web and messaging friends. With the new app pairs system, you can only split the screen between two select apps, and you need them both to be open before you attempt it - if you want to swap out the bottom app, you have to unpair the two apps and repair the top app with a different one, which just seems worse in almost every way. It made attempting to multitask a nightmare which takes up a lot more time than it requires[1] - and despite multiple complaints for the last few years, Google hasn't commented on it whatsoever[2]. It also generally coincided with when Google made YouTube Premium let you watch videos in a window or in the background on mobile.

Again as someone who's always liked Android and was excited about new updates, I've hit the point where I can't bring myself to look at anything new because of all the recent decisions, UI changes, and introducing confusingly odd features which I don't have the ability to disable or customise to my liking.

[1] https://imgur.com/IXmpubM
[2] https://issuetracker.google.com/issues/210345474