No proof = scaremongering

Yes, Signal is not perfect, but I have no reason to believe that they are in any way compromised.

How private are our supposedly private communications, and who ultimately has the ability to access them?

That’s what open source and encryption are for

tbf, I’m not sure about older Fairphones (I have a FP5 and I needed to do that)

On Fairphone, for every OEM unlock you need a working internet connection, and for the first OEM unlock you need to get an activation code from Fairphone using your phones IMEI/serial number. So I’d say this classification is correct. I also have a Fairphone and everything worked without problems, but it is still 100% controlled by Fairphone even on already sold devices.

Not sure about older Fairphones. I have a FP5.

See https://www.fairphone.com/de/bootloader-unlocking-code-for-fairphone