@arubislander Good thought. Perhaps I should have mentioned that I use Tor (or a public computer) because this site forwards user data to Cloudflare.

I believe that live a session won't prevent fingerprinting/canvassing, regarding my accessing this site; and and not help regarding the problem of 'missing files' in the Google bonito file.

Any more ideas?

@arubislander Mate Mint 24.04.2; kernel 6.11.0-26-generic

I don't know how to update my post, so I'm trying this.

I finally used a zero-privacy (public) computer to visit Google's developer website to get bonito. After floundering through multiple, inconsistent, instructions on how to downgrade, and multiple visits to Google, I saw a .sh file for the first time. It seems that Google hides everything older than Android 11 even with minimal privacy enabled on my computer. Maybe that could be mentioned somewhere.

However, the .sh script aborts saying that fastboot is out of date. I had just installed it for the first time, and my Linux system says that it is the latest version. I wonder if the "Copyright 2012 The Android Open Source Project" script is out of date.

I executed the script commands manually:
fastboot flash [the bootloader]
fastboot reboot-bootloader
fastboot flash [the radio]
fastboot reboot-bootloader
all is good so far
fastboot -w update image-bonito-pq3b.190801.002.zip
checksums match; I get the following:

extracting android-info.txt (0 MB)...
extracting boot.img (64 MB)...
target reported max download size of 268435456 bytes
archive does not contain 'boot.sig'
archive does not contain 'boot_other.img'
extracting dtbo.img (8 MB)...
archive does not contain 'dtbo.sig'
archive does not contain 'dt.img'
archive does not contain 'recovery.img'
extracting system.img (2278 MB)...
W/ziparchive(74369): Zip: unable to allocate 2389524784 bytes at offset 0 : No space left on device
failed to extract 'system.img': I/O error

Note several lines of "archive does not contain"

The "Flashboot Mode" bootup screen on the Pixel says:

Product revision: bonito MP1.0(US)
Bootloader version: b4s4-0.1-5653622
Baseband verison: g670-00011-190411-B-5457439
Serial number: 938AX05MER-
Secure boot: PRODUCTION
NOS production: yes
DRAM: 4GB Hynix LPDDR4X
eMMC: 64GB SKHynix
Device state: unlocked
Enter reason: reboot bootloader

I assume that I do not need to install 1.7MB of Android in order to nuke it, so I ran the UBports installer on the phone as it is, from my computer. But the freshly downloaded-for-the-first-time .deb file won't install (ubports-installer_0.11.2_linux_amd64.deb). I get the following error messages:

dpkg: dependency problems prevent configuration of ubports-installer:
ubports-installer depends on heimdall-flash; however:
Package heimdall-flash is not installed.

dpkg: error processing package ubports-installer (--install):
dependency problems - leaving unconfigured

It seems that heimdall-flash is for Samsung phones, although I downloaded the UBports Installer from the Google Pixel 3A XL page.

It gets better: every time I open this thread, my Linux OS restarts, and I have very limited access to other systems at present, making this site difficult to use. I really appreciate the quick responses, but I need more input. Where do I go from here?

Re: I have to downgrade from android 12 to 9 but...