Hey a MI 10 Ultra here, I've been using my phone since September and from my experience the MIUI v12.0.15.0QJJCNXM worked like wonders, (this is the latest android 10 update), but I don't recommend using the new android 11 update as right now it has few bugs which can do a lot of problems for you, as of twrp you cannot flash the rom without it but in the future you'll get all the updates trough ota. also Im using stable branch forgot to mention. also twrp is a lot better then the stock because you have a lot of advanced options for installing stuff and doing backups or saving your device from getting bricked.
this is the link for the stable rom :
https://sourceforge.net/projects/xi...0Ultra_V12.0.15.0.QJJCNXM_v12-10.zip/download
I prefer to use the stable as its more unlikely to get bugs and stuff but if you want to get all the new features without worrying about bugs or problems that might occur you can use the weekly
here are the instructions for flashing twrp and the rom.
as for the android 11 update as of now it has few big problems but they will be resolved in the future and then I recommend you to update.
also you'll need to unlock the phone which will take at least a week (that's the minimum time until Xiaomi unlocks your phone when you send an unlock request) so in the first few days using the phone before the rom you'll encounter few problems but trust me after flashing the rom everything will resolve and your experience will be the best on your beast of a phone
if you have additional questions feel free to ask)
also don't forget tp backup all of your data after every time you flash and install stuff as mostly it will get removed but in the future the ota updates will not delete your data but still a backup is always recommended)
- Israel
UPDATE:
today the developers reuploaded the latest android 11 stable build which fixed the major bug causing many apps crashing and not working as intended, so instead I recommend you to go straight to android 11 as It looks its ok now but I'll warn you the new android experience will differ a bit from 10 but you get used to it pretty fast so don't worry much about that, anyway here's the latest android 11 rom: [MIUI V12.1.1.0.RJJCNXM_v12-11.zip]
if you'll encounter crashing apps then going to settings then pressing on the version will lead you to the update screen where you'll get the new fix update which will fix the crashing.