Porteus

I've installed porteus v5.0 but the Bluetooth headphones are not getting connected.

I'm getting error

"Connection failed: br-connection-profile-unavailabe"]

I can connect with my phone. There is no problem for that. But can't connect to headphone.

I've been using porteus 5.0 rc1 previously because Bluetooth headphones where working in that version.
Even after releasing rc2 and rc3 I wasn't able to update because of this Bluetooth audio issue.

It's a great deal for me because there's no other way for me to hear audio.
Please help me.

Lacking any hardware specifics, and if you can't seem to get anywhere, maybe try option b:

Invest in an inexpensive usb<>bluetooth dongle that is certified to work with Linux. Many available online.

One of the advantages is that it might be likely much more performant / secure than the one on your older / strange box.

I've used this slacker modern usb dongle solution before with not only bluetooth, but with wifi and audio as well. Since I use Porteus in a portable format, I just pull the dongles out of my bag of tricks when necessary.