ROM flashes – TWRP asks for password – Data partition can not be mounted

I would like to install an open ROM like AospExtended on a new Xiaomi Redmi Note 5 with standard MUI. To avoid problems with Xiaomi's anti-rollback mechanism, I want to launch TWRP, then copy and permanently install its image, as described in many posts as described here.

But TWRP can not mount my data partition, it asks me for a password. I had no set. Regarding this post, I tried to set a password for the lock screen. Although he has the same problem with an older version of Android, it does not accept the password.

Some threads like this recommend OrangeFox instead of TWRP. However, 9.0-1 shows the same behavior:

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With OrangeFox 9.0.2 no password is requested, so this seems to work. But why does not it work with TWRP? This post said it is fixed in 3.2.3_1, Because I've booted 3.3.1-0 so:

> .fastboot.exe boot D:Downloadstwrp-3.3.1-0-whyred.img

This fix should be included. To work around this problem, try out OrangeBox (especially with regard to OTA updates that OrangeBox has not yet tried). But I would like to know why there are these problems with TWRP and how they can be resolved.

I have used TWRP over time with different devices and it has always worked well (even with OTA updates).