Bluetooth headphones can no longer be connected?

I've had the problem for a long time. I can't connect my over-ear headphones to my cell phone, my laptop or anything else. And when I go to scan for Bluetooth devices, I don't see it either

Edit and solution: I tried to find something in the user manual, I didn't find anything in German, then it occurred to me that my headphones still run via NFC, I then connected them to my headphones and since then it has been connecting normally again Bluetooth (at least on my cell phone).

And what is the question now? When everything works again.