I am a former embedded system engineer. I tried to “degooglize” partially my Fairphone 4. Here are the steps, compilation of different topics and information already available. For more details about the different steps, go to the #fp4guides page.
First, you need to unlock the bootloader. Here is the procedure, which is the same for fairphone 3 and 4 :
Don’t forget the command : fastboot flashing unlock
Then, install Magisk and root your phone, explained there : Fairphone 4 - Root | XDA Forums
Then, enable signature spoofing installing Riru, Riru LSPosed + Fake signature fork :
Rom is deodexed so no need to patch…
Then, use Magisk to install NanoDroid-MicroG : NanoDroid/Installation.md at master · Nanolx/NanoDroid · GitHub
You don’t need to delete Gapps, NanoDroid will do. I only tried installing the MicroG version of NanoDroid, perhaps you want the full version… If you do so, please tell me the results !
You can further update microG by downloading the last apk on the official website : Download - microG Project (Version 2.22 versus 1.17 in NanoDroid)
Optional : Install TRWP. TWRP for Fairphone 4
Backup the original boot by launching : fastboot boot image_twrp.img, saving with the backup function of TWRP…
Perhaps this tutorial is a bit short, don’t hesitate to ask me some details.