Yes, i believe Mi 11x had different screen.The difference is the model. Poco F3 and Redmi K40 are the alioth model, while Mi 11X is aliothin. Most custom roms makes the distinction between models at flashing, who isn't the case for stock. There's the slight chance to brick the phone while flashing the China version, plus the baseband aren't the same.
If you like to test pure MIUI instead of Poco MIUI, why not instead extract the desired APKs in Mi 11X ROM and replace them in your Poco F3?
The idea is to keep it simple instead of tweaking, the K40 firmware will be the way to go, but I'm not sure that firmware has Google services.
I've read the best firmware is the one for China, and xiaomi.eu is based on that firmware but tuned for other markets.
But that imply unlocking, installing twrp, etc so it's not that straight forward