TWRP for Fairphone 3

Absolutely not on the Fairphone 2.

Not with Android 8+ encryption.
Official TWRP 3.2.3-0 was able to handle up to Android 7 encryption.
Current official TWRP 3.3.1-1 should be able to handle up to Android 7 encryption again after decryption somehow broke inbetween (I didn’t check myself anymore, though).

For Android 8+ you can try your luck with this custom TWRP build here, it may or may not decrypt for you … Custom TWRP 3.2.3 to decrypt Android 8/9 encryption.