@moodroid ... I just bought some 3a and 3a XL for a project where I needed a Linux Phone ...
And my first experience was to be 4 hours fighting and finishing with a "bricked" 3a ... ahhhh ... just that was not bricked and I didn't understand several things about the process (I am writing my own manual with the details).
At the end, that Android 9 permanent Google splash screen after using the flash-all.bat is annoying, but not wrong. Just need to continue with the UBports installation and at the end you will have an operational Ubuntu Touch phone working.
Other thing .... the current Google instructions for backport are USELESS, as they already erased the information about the 3a or 3a XL. There is a WIRELESS version that doesn't work because it is not possible to downgrade the phone ... (Android limitation), so you need to use a FACTORY version, unpack the ZIP file and follow the instructions, to finish with the bricked phone. I found one, but after so many URLs I am not sure where I had it ... could some official Touch source to publish an official FACTORY URL for 3a (sargo) and 3a XL (bonito) images? ... again, don't say that read the Android references, because they are no longer working with these Pixel phones.
It seems that UBPorts just needs the phone to have some Android 9 things there. And well, I even erased all the phone, but rebooting it and playing with Power and Power volume buttons, makes the PC script to recognize the phone and deliver the Android 9 version.
What about another Android version? ... in my initial desperation, I also tested that, but the installation fails. So cool your head a little and just do the things with calm and everything happy.
The Flash Android tools downgraded a 3a XL without any trouble, Just Development mode, USB Debugging and the OEM Ulocking, and to accept some questions here and there and ready, Android 9.
The only I need to figure is how to turn off the Unlocking option since I have no more Android in the phone and I don't need Android there again ... maybe one of these days 