Got hold of a Mi A2 today, so ubuntu touch must go on it, so here are my observations for the install.
Two computers ready, one with windows 10, USB 3.1, the other with Ubuntu 21.04, USB2 and 3.

The phone was on Android 10, set OEM unlock and USB debugging, booted to bootloader and did :

./fastboot oem unlock

(windows 10 Powershell), all going good so far. Ran the installer and it failed.

Switched to the Ubuntu machine, and couldn't get the vendors image file to transfer. Put it in the root of the home folder and it just would not go. So couldn't go any further there, so back to windows 10.

So back on windows, I could not get it to pushing files to the device, it failed every time with an ADB issue and wouldn't write to the partitions.

Dropped back to Android 9 and had the same issues. I then tried:

./fastboot oem lock
./fastboot oem unlock_critical

This locked the bootloader again then the critical unlock unlocked "critical" partitions so they could be written too.

Still failed with an ADB issue, so I updated my Android Studio and voila, installed like a charm.

So another phone to test - only thing so far is the front camera switches on the light (sore eyes).

So again, moral is to persevere, persevere and persevere. Installing boot files and halium-9 recovery takes about 5 minutes and there appears to be nothing going on. Leave things alone, till the installer tells yo to go to the next step. After that it goes pretty quickly compared to some other devices.

I would like to finish off by thanking the developers, these forums and XDA-forums who give some great advice and ideas. Keep up the good work.

I misread and thought it said Redmi Note 7 (lavender) which is on the installer. It has slightly different hardware to the Redmi Note 7 pro.... Apologies (full of cold).

Deleted my last post for getting mixed up. These are my EE settings for MMS:

Used for: MMS
Name: Picture Message
APN: general.t-mobile.uk
MMSC: http://mmsc.t-mobile.co.uk:8002
Proxy: 149.254.201.135
Proxy Port: 8080
User name: user
Password: wap

These are my EE settings for INTERNET:

Used for: Internet
Name: Internet
APN: general.t-mobile.uk
User name: User
Password: mms

Have you gone back to Android? Go back to Android and cycle through battery charging for a few weeks. If the battery is OK in Android, try UT again. I had null battery stats, but have not had time to put my Android tablet back on UT.

Yes, it is still an absolute mare to get running again from a flat battery.

@rth If you did that before and it didn't work, then start again. Also you shouldn't have to mess with the slots, unless you had another Android based ROM that required it.

I have four at levels, one is good, one has the UT battery issue (always showing 100%) and two have smashed screens (scratch devices, if I brick them, no great loss). Gives me a chance to test and benchmark and find any issues, of course time permitting, which at the moment I don't have. Once done, I will generally refurbish and sell on (usually at a loss, but I get done what needs for me to be done).