While we are on the topic of Signal, does anyone know if it's possible to have a lock/PIN to open the Signal app itself that's different than your device lock/PIN?

Threema has this feature and it's reassuring to know that people can't open my chats when I hand my phone to someone. Or if I give the device lock/PIN to someone I trust for backup purposes but don't want them to have access to chats themselves.

Last I checked this was not possible with Signal (at least on Android).