Real life isn't that clean. Security is about layers and making things as difficult as possible; there is never a single step which will fully protect you from everything

Because if you do, you just got Cellebrite'd. Your entire phone is compromised, now and going forward.

It s litteraly on the signal option "Require acces code to open signal"

I have App Locker in settings iy let's me use a fingerprint unlock on any apps I want, I assume it's a stock Android feature.

Some Android devices has app lock build in.

There's Private Space, but that's not ideal for a general-purpose messaging app because notifications are suspended when the space is locked. Signal also has the option to require the same authentication method as your screen lock in order to access the app.