Place the wrong fingerprint you've previously registered in order to factory reset. When they force you to put your finger to the phone, you just make the thumb your duress fingerprint or thumb placed upside down or some other finger, etc.
-Helps when you can't get your phone into Lockdown mode or BFU before its taken.
-Helps when CCTV or shoulder surfing sees what your pin is before obtaining your phone returning you right back to just fingerprint and no + pin unlock.
As another feature for both Duress Fingerprint and Duress pin/passphrase, one should be able to randomize it. In settings, you can choose a custom pattern. Place thumb once, place pinky next time, place index finger next time, fail to do it right sequence of your own choosing and it factory resets/auto reboots (your choosing). It's not enough to go "ok I know his thumb is registered and has a pin of 582634 from CCTV" anymore. Same with multiple pins that actually unlock if you're willing to memorize more then which finger is now its turn to be placed on the screen. 75753 first, 47284 second, 58273 third, 736523 fourth, third one again as fifth, fourth one as sixth, second one as 7th, 1st one as 8th, back as first as first second as second, so on. Do a correct pin when it's not yet its time in the sequence and factory reset or auto reboot. No cctv camera is going to be able to capture all your registered pins and fingerprints and in the right custom pattern of your choosing making it Fingerpint + pin + sequence only of your knowing that CCTV and shoulder surfing is too under powered to sniff. This successfully makes the strengthened fingerprint + pin not return back to security theater as GrapehenOS project states as strong requirement for any security feature which brings us right back to forcing them to place finger on screen once they get your pin from CCTV under current implementation. Just like that GrapheneOS can protect from CCTV cameras and shoulder surfing thanks to the work already done.
I read somewhere that any improvements to fingerprint + pin unlock would be a low priority feature and thankful for whats already offered but if there's interest in making it as secure as can be I'm fine with whatever the priority,