You have to unblock it, you will have to apply for it and wait a week to do it.
I flashed miui 13 using the twrp version from this link https://xiaomi.eu/community/threads/mi11-ultra-pro-twrp-3-5-2_11.63457/ . miui 13 download link- https://bigota.d.miui.com/21.12.27/miui_VENUSPRE_21.12.27_86888c626e_12.0.zip . Instruction -
Very similer to the last a12 beta performance, faster then miui android 11 but has the same bugs as the last a12 miui 12 beta . There are new wallpapers and widgets.
i took the risk and went for it. first impression my heart was pounding hoping it wouldnt brick my device. i was on latesr xiaomi eu stable build, install the twrp recommended here, formatted my data, flashed the zip, it output some errors but it flashed i formatted again, twrp said there was no os installed but i just rebooted and it booted fine. and yes MIvideo is not working. here some screenshots. Also there are some changes visually and animation wise and at least as a first impression i does seem more fluid and responsive.