xiaomi.eu was a good rom until it EOL’ed my phone. I thought, why not use the global rom from now on? My phone is compatible with Global, right?

Wrong! It boots all right but you won’t have service because the rom doesn’t support the phone’s modem.

If Global won’t work, China rom will, right?

Wrong! This rom doesn’t support the modem either.

WTH!? Turns out there are different versions of the phone for different Chinese carriers, this phone is for China Mobile, and none of the roms on en.miui.com is compatible with the phone.

What’s the solution? Use fastboot to flash only the modem support package (driver?). It should work, right?

Partially wrong. You get service all right but settings won’t open and any attempt to uninstall an application will reboot the phone. What’s wrong?
The modem support package is wrong, that’s it. I don’t know why but all the packages I found online were incompatible with the phone.

The solution:
Take the modem support package from the xiaomi.eu rom (thanks a lot for the file guys) and use this command to flash the file:
fastboot flash modem NON-HLOS.bin

To put the phone in fastboot mode turn it off and then on when volume down is held until the phone vibrates.
Here is the file extracted from the xiaomi.eu rom.

Everything works now. Took me a day of fiddling but it was kinda fun. Hope it helps.