Source: https://dl.akr-developers.com/?dir=skkk/TWRP/A12/v6.0_A12
Download: [REC_BOOT]3.6.2_12-Mi10Ultra_v6.0_A12-cas-skkk_7f10db0d.zip
I use this one to flash xiaomi.eu_multi_MI10Ultra_V13.0.5.0.SJJCNXM_v13-12.zip without any issue and boot correctly
There is one, but I can't find download link :(
https://weibo.com/xinkid520?refer_flag=1005050010_
MI 10 Ultra Android 12 TWRP3.6.0 Auto Decrypt 2021.11.18 Update
It's xiaomi's issue, related to questions and feedback function app.
https://www.xiaomi.cn/post/23323630
Someone solved it by sending feedback "with log"
After that, other's in storage will be fine.