My cheesy experience report

ROM version: 18.1
Update: 2021-11-29
My phone was really getting old, and slow. My battery drained quickly, and I needed to reboot often to get it back to being speedy.
I wanted to install a new ROM for a long time, but was scared of having no phone. I was afraid to forget to backup stuff.
Then I had a good day. I said to myself, now I confront that anxiety!
So I set forth, and unlocked my bootloader. I got my phone into fastboot mode, only to find that I got greeted with a black screen and a blue LED lighting up. I was afraid - does it not work, did I do something wrong? But it was normal, that's how fastboot shows itself on this particular communicator.
So I unlocked, with old Sony's instructions, telling them my IMEI and getting an unlock code in return. I told the magic number to "fastboot oem unlock", only to find, it responded with silence.
I waited impatiently. Should I reboot the phone, should I pull the plug? I did not, and was rewared for my patience, with an acknowledgement after about 4 minutes. The phone was free.
I flashed the most recent TWRP recovery, and replied with an enthusiastic "success". The TWRP quest giver said, "this recovery might get replaced upon reboot!". I got afraid. I rebooted my phone, and saw, oh no, I can't boot my old installation anymore, it was the old nefarious stock ROM, reset to factory defaults!
There's no way back now I concluded.
Happily, I found that my phone does not replace its recovery upon reboot. I got into recovery by turning off my phone, and pressing the volume down and power levers of my magic telecommunicator.
Only to find that, now how do I get the ROM and gapps on the phone? Trying to get "adb" to work inside TWRP, I got greeted with a "no permissions" error. I concluded, this can't be a problem on Linux' part, as adb did work before with my old ROM.
The hardware method it was, swapping in and out the phone's microSD card, while being glad that this ancient phone still supports this technology.
It worked, it booted, I put the gapps zip file on the phone, rebooted into noble TWRP, installed gapps, rebooted. Only to find myself with permission errors from google services, which I could not grant.
Only later I realized, I need to install gapps
before the first boot.
So I did. Hence it was recommended, "stock gapps" was what the decision fell on. Only to find that I got greeted with a black screen and only a back button during the first endeavour to provide the search giant with my data (maybe something like
this).
I tried with gapps nano, I think, but my memory is covered in mist. I got greeted with a Wifi chooser, and only a non-working speech input and no other keyboard available. I could not provide the secret passphrase.
I tried again, wiping, flashing this worthy ROM, flashing gapps, this time pico. I tried these four steps a lot of times, swapping the microSD card in and out.
It worked.
I could provide the mighty "no longer don't be evil" giant all my belongings, as I usually do, and was presented with a way to restore my data and to access the Play merchant.
So now I needed to restore all my backups. This all worked. Mostly. Not really. But at least some of the time.
Whatsapp shouted: "I don't see your backup!". So I can't restore it. Fear set in. Will I lose years of message logs?
So I deleted Whatsapp again. And asked the "no longer don't be evil" giant for help, for one little-noticed result to explain, why the backed up data couldn't be found on Android 11 (
https://android.stackexchange.com/a/241647).
It worked. The backup was discovered. Everything worked. Apart from spell checking. My phone is new again.
TLDR: thanks a lot to all the creators of this ROM! Paying with NFC is working. Battery life has improved. Everything feels a lot faster. I have a lot of fun using my old phone again, with Android 11, without putting a strain on the environment. Also I did not have to spend money to buy a new phone, to get security updates that are newer than 2019, for phone that was first released in 2017.