Fairphone 3 and 4 have broken bootloaders that trust test-keys for Android Verified Boot: https://forum.fairphone.com/t/bootloader-avb-keys-used-in-ro...

And they have similar limitations to what I do here with regards to firmware support, as they offer longer support than Qualcomm actually does for these chips used.

The only devices with proper aftermarket OS support and five years of updates are the Google Pixel 6 and 7 series.