This is not true, as I have a resigned lineagos running on a pixel 2, and even aura (razer phone 2), which is once supported by divestos with relocking.
Pixel 3a XL might be special someway, but according to #299 and #274, only resigning stock google ota packages would be problematic, so resigning iodeos builds should be okay.
#299 is misleading someway, as it mixed up device support and specific (google stock) ota package format support.
Thank you for the great efforts you put into building these.
Are you using Seedvault as a plan B? Rik seems to think it will update without losing data.
Thanks @rik. Here are the detailed steps I used to successfully update my Pixel 4a5g unofficial build from Iode 6.7 to Iode 7.1 without losing data:
Back up phone, just in case.
Connect phone to computer via USB
Open a terminal
Confirm authorized ADB connection with adb devices
Download the IodeOS…zip file for the 7.1 unofficial Rik build onto computer
Boot Pixel into recovery mode from computer terminal using adb reboot recovery. This re-confirms adb connection and provides a clear path to Recovery Mode.
Sideload the IodeOS…zip file.
On the device, select “Apply Update”, then “Apply from ADB”.
On the host machine, sideload the package using: adb -d sideload /path/to/zip
Wait for Pixel to show the “Signature failed” error. Choose “Yes” to continue to load anyway.
Wait for Pixel to show “To install additional packages, you need to reboot recovery first. Do you want to reboot to recovery now?” Select NO.
Select “Reboot System now” from recovery main menu.
Check IodeOS system update information on the Pixel to confirm that the update was successfull.
Thanks for the info. Yes, I use Seedvault as a backup; a backup can never hurt.
There are two different cases here.
The case you describe: unofficially iodeOS from v6.7 to v7.1 via adb sideload without losing data.
The case I mean: unofficially iodeOS v7.1 to official v7.1. Rik tested this and ended up in a boot loop.
I tried the same and did a factrory reset via recovery, but the unofficial 7.1. did not install because of key verification failure. I didnt get a bootloop then, but just landed in the old 6.9. official ROM.
What did I miss?
You need to “proceed anyway” when you are warned about the key verification failure, this is due to now using a different build key as described above. Thanks to @HandyTravis above a few posts for writing up the details to move to 7.1.
I would have done so (as usual…), but the question didnt come up!
OK I didn’t fully appreciate that you were trying to go from an Official down to an Unofficial build. I don’t know of many that want to go that direction, but hey thanks for considering my Unofficial build preferrable 
But yes I think this can re-confirm that going both directions between Unofficial and Official builds just won’t work without a full clean re-install.
I know how to sideload the .zip, my problem is that I wasnt asked if I want to confirm the signature failure.
I dont care much about unofficial or official, but the official build 7.1 isnt available yet.
At least not here: sunfish · master · ota / release · GitLab
Edit:
The recovey errors are the following:
error: recovery: failed to verify whole-file signature
Update package verification took 63,5 s (result 1)
error: recovery: signature verification failed
errors: recovery: error: 21
The Lineage 23 (Android 16) builds for sunfish arrived just at year end (after the v6.10 official builds were published). I would suspect that iodé v7.x official builds will be coming.
But if you want to migrate from official to unofficial I think you need to do a full factory reset and re-install (including re-flashing the boot image just to make it all consistent).
Sorry this post got held in our queue. But put simply, no devices were abandoned, instead official builds were never made for them, likely do to the lower availability of them in Europe, and due to storage limitations.
Note, by the way, that 2 of the 3 ROMs you list above dropped official support for Pixels older than that the 6 series, so all the devices you use as examples are not supported by them.
Sorry for being ignorant but could you point me to an instruction of a full factory reset as you mean it?
Essentially you need to do a clean installation. In the table at the top, follow the link in the first column to open the LineageOS installation instructions for your device. You then use the files provided as part of my custom builds instead of the Lineage provided files.
(For sunfish this means flashing dtbo.img and boot.img, then boot into Recovery and sideload the .zip)
But if you are on the “Official” ROM right now you just may want to stay on it, as I note it may be soon that iodé 7.x builds are available for sunfish:I didn’t quite understand if you are wanting to change to the Unofficial ROM in order to have adb root for full backups or what is the motivation to move away from the Official builds?
Thank you Rik.
I guess your suggestion to be paitient is spot on, I do not need to change to the unofficial build, I was just so excited that there is Android 16 available and wanted to run it. And on the way I tried to learn and understand some things. And I probably did, but as so often more question arise 
I got confirmation from the developers that there will be official builds produced for the Pixel 4 and 4a starting with v7.2 due shortly.
Still waiting for taimen update. Any plans on this? Would be great to have updates on a regular basis. Last update is months away.
Any plans on making an official build for the pixel 9 pro fold and pixel tablet?
The Iode folder appears to have been deleted. I am not seeing any unofficial builds. All the links in this post are dead. Yikes! I hope I am overlooking something obvious.
It’s not obvious, but the unofficial iodeOS builds have moved. They can now be found in this directory on the LineageOS for microG download server: https://iode.lineage.microg.org/
I’ve added a note to the first post, but I am not going to spend my Sunday afternoon editing he links in the table - better things to do