Replying to myself, I’ve taken the chance (of being the only one I know locally) to order an FP5 - transparent edition - to help show the “Why?” to others.
I just received it a few days ago, and it seems to work fine with Vodafone Portugal.
Just tested the basic, make/receive voice call, send/receive sms (without RCS), use some mobile data, and all seems to work.
(Did not test the speed of mobile 5G data, and neither tested services under weak network coverage, yet).
The phone migration went smoothly, and I seem to be able to do everything I did with the FP3 (use Android auto in the car with an USB cable, use Bluetooth in the car, make payments scanning QR-codes, etc).
Performance seems to have gone back to acceptable levels. The instant messaging app notification huge-delay seems to have went away, but it needs more testing (having more people contacting me when I am not at the work PC).
Now it is just a matter of getting used to new features (face unlocking, tap to wake up, getting used to the new fingerprint reader, dynamic bright - turned off for now as sometimes the screen gets very dark, etc…).
I miss the 3.5mm audio jack, but I will probably buy an USB-C headphone soon (more money for the same feature
So, I recommend FP5 to anyone needing an upgrade (or a new Android phone).
(FP3 will become my backup phone body, pocket tablet, and in a few months, until I have courage to apply a factory-reset, then maybe use it for games).