Is there a secure, hidden screen recorder that can be recommended

I'm on a samsung phone, 5.1.

Secure, as in no one can see the recordings? No. You can always hide them though.

Hidden? From some people, maybe, from others nothing is hidden.

On an older phone, still running Lollipop, probably not too much out there will still run.

Are you worried that someone is using your phone without your permission? Or are you trying to install this on someone else's phone so that you can snoop?