This is a known issue, specifically for the Mi 10 (umi). The TWRP that is with the weekly ROMs does not decrypt your data. Therefore you are limited as to what can be done with this, for instance, installing a new weekly ROM can be done through USB-OTG. This is putting the ROM onto a USB memory stick, and plugging it into the Type C socket, and changing the storage source during the install process.
Alternatively (you need to be very familiar with the Fastboot process for this), you can BOOT ONLY into another version of TWRP.
This is version 3.4.2b-1206 -
here is the link. The Fastboot command is:
fastboot boot recovery-TWRP-3.4.2B-1206-XIAOMI10-CN-wzsx150.img
But,
DO REMEMBER - this is only for booting (temporary). DO NOT FLASH this version of TWRP.
This decrypts and gives access to all of the basic TWRP functions, and will work with a pattern. It takes about 70 seconds to load up. You have to sign in with a pattern, not password. And you have to click a few mms beneath the target.
[Edit: How confusing is this! The version above is a different 3.4.2b-1206 that is now being installed with the weekly ROM. Do not get them confused.]