I feel like this is one of those situations where you might be able to use something like an NFC tag to force your phone into a locked state where it would require the pin to unlock.

I think an SOS style pin input is great in theory but I don’t know that most people will use it because it’s not necessarily going to help in places where you might be required or forced to give up biometric unlocking credentials (some countries make it so there is not a legal way to refuse to give up your fingerprint or face scan etc). This isn’t any easier than setting a lockdown key combination etc. Currently on my phone the lockdown is set to enable if I press the power button and volume up key at the same time and I think it’s similarly easy to do on iphones.

I feel like this is one of those situations where it also might be a workable idea to use something like an NFC tag to force your phone into a locked state where it would require the pin to unlock. If of course lockdown mode can’t be enabled on your device using a key combo and you have NFC available.