Looking at the PostMarketOS Wiki for Fairphone 5, it looks like audio, camera, calls, nfc, and fingerprint are all partial or broken.
themightycat@ani.social has been able to get audio, calls, and NFC working on the Fairphone 6. According to him, he is currently working on the camera(s) with another developer and also going to try and get the fingerprint reader working too).
I'm not sure how compatible they are, but it might be worth asking if he could look at porting the Fairphone 6 to Fairphone 5 for people. Alternatively, all his additions are open source, so someone else could take a look and see if they are portable.
Edit: corrected TheMightyCat's code repository link.