Well, it doesn't look too bad when the background partially breaks. That happens when I switch between landscape and portrait mode - it either gets zoomed in, or fit in letterboxed like this:

This is basically the only image that looks OK in both states.
The global version of MIUI is full of such bugs. Previously I had the EEA version, but after both motherboard replacements I got the global version. For example, the lock screen wallpaper gets stretched top-to-bottom after reboot, but it disappears on locking. The home screen wallpaper was a pain to figure out. Native resolution gets slightly zoomed in after changing brightness, and any other resolution also gets stretched top-to-bottom, but that lasts. My workaround was thus to take native resolution rectangle, and fit the desired wallpaper into it, slightly smaller in center. It's fuzzy, but at least it's the correct aspect ratio.

Anyway, plenty of bugs in MIUI. I could try a custom ROM, but I already have everything set up, and I can mostly work around the bugs. MIUI is also one of the worst systems privacy-wise...

Also, I use Firefox on desktop... and in Termux because it's the only way I can do overnight file uploads as mobile browsers just crash after a few minutes of locked screen.