GrapheneOS provides users with the ability to set a duress PIN/Password that will irreversibly wipe the device (along with any installed eSIMs) once entered anywhere where the device credentials are requested (on the lockscreen, along with any such prompt in the OS).
The wipe does not require a reboot and cannot be interrupted. It can be set up at Settings > Security > Duress Password in the owner profile. Both a duress PIN and password will need to be set to account for different profiles that may have different unlock methods.
Note that if the duress PIN/Password is the same as the actual unlock method, the actual unlock method always takes precedence, and therefore no wipe will occur.
something something destruction of evidence
What evidence?
Alternately, it could unlock the phone while also erasing specific parts of it, like message history and call logs, potentially replacing them with something you’d set up previously.
Edit: and obviously it would disable the duress pin and set the unlocking pin to it.
Depends on what you did! Say for example they’re using Graphene to harass/paedophilia then they already have a copious amount of evidence on hand since they are there.
For organising peaceful protests that seems less of an issue and the other end of the chats is the weak link.