@madas Yes you need to create Xiaomi account to be able to unlock phone's bootloader. What 155 hours long process means, is that it is some security measure from Xiaomi, if I understand it right. When you try to unlock bootloader for the first time it fails and tells you to wait 155 hours (1 week) and after that time you should be able to unlock bootloader without problems.
As for point number 3: Phone must be running Android 10, for system partitions to be in correct place for UT installer to work, otherwise you could end up bricking the phone. So if you are on version 11 you need to downgrade, there should be links to Android 10 ROMs somewhere in this thread.
For example I used this ROM:
Redmi Note 9 Pro Global EEA
Point 4: You must downgrade if phone is running version 11 or newer.
If there is something else I missed from your post just ask.
EDIT: Phone must be running Android 10 to be able to install UT.