This is a gem of an app that turns your android phone into a Bluetooth mouse and keyboard for other devices.
Edit:
What makes this app different from other “remote control” apps? Most of them need a “server” or “companion” app to be installed on your other device. This app doesn’t. It just needs pairing via Bluetooth.
I use it to control an Android tv box. As you know typing with on-screen keyboards on tv screens is an absolute pain.
With this app you can type anything on your smartphone and send it to any text field on your other device. You can also add cistom keys and key combinations. Note the CTRL+A shortcut key i have added for select all in the screenshot for example.
It can also work as a mouse with customizable buttons.
https://play.google.com/store/apps/details?id=io.appground.blek
My tv is my second monitor. I have used this app almost daily for an entire year. It’s pretty good. The custom layout needs some work. Either that or I’m too dumb (it’s probably that).