Look for the latest twrp-3.5.2_9-0-davinci right on the official TWRP site:
This is the Team Win website and the official home of TWRP! Here you will find the list of officially supported devices and instructions for installing TWRP on those devices.
twrp.me
Also, for the Magisk Installation instructions on the official Magisk Github site:
The Magic Mask for Android. Contribute to topjohnwu/Magisk development by creating an account on GitHub.
github.com
And important: You have to patch BOOT (not Recovery) image. There is a note/exception there talking about, but probably not clear enough that it applies to Xiaomi
At the end, in Magisk app, Settings, enable MagiskHide (hide Magisk from various forms of detection) option - it's no more enabled by default
Anyway, I have Mi 9T too with Xiaomi.eu 21.5.12, latest TWRP twrp-3.5.2_9-0, and latest Magisk v23 installed by patching and flashing the boot.img, and everything is ok