Honestly, i also want to know why so much hate on MIUI?

Here's what I think why people disliked it:
1. Pre-installed app such as FB, Linkedin, Booking and some chinese apps. But it is easy to uninstall it, just 2 clicks away.
2. Advertising. Just need to go to each individual components and turn off recommendations. If i recall correctly, 5 or 6 places.
3. Wallpaper carousel. If you use this, probably you will get in-app advertisement. Just don't use this feature, easy.
4. Bloatware. TBH, i think Samsung's bloatware is even worse. Also MIUI is using Google stock dialer and messaging app.
5. Home launcher. It is known that MIUI did not encourage you to use other launcher, it let me use Nova launcher but navigation gesture won't work (there is a workaround for this). But personally, I'm quite comfortable with MIUI stock launcher, especially when you use app drawer mode, the search field is located conveniently at the bottom, near to your thumb. For other stock launcher, their search field mostly located at the top screen, which is very inconvenient especially when working with single hand and your thumb can't reach that search field on top.

Full disclosure, I'm currently using Mi10T so my opinion could be biased. But i also have tried S20 FE with OneUI 4, and Motorola Edge 30 Pro (and non-pro version) with their close to vanilla android UI, but in the end I'm back to this old phone.