Update: The button labeled 'Start Bluetooth Pairing' now changes to 'Stop Bluetooth Pairing' when clicked and 'HiFiBerry' now shows up under available devices and pairs correctly. Unfortunately, the only thing I did to it was transfer the SD card into a different Raspberry Pi 4, which should have had no effect, so I don't know why it's suddenly working.
I have just finished setting up HiFiBerryOS on a Raspberry Pi 4 and am trying to use the bluetooth receiver function. I'm operating it through the hifiberry.local web interface. Spotify Connect is working flawlessly, so I know that HiFiBerryOS is functioning.
In the Sources > Bluetooth tab, it says bluetooth is enabled, and 'open for pairing until stopped'. The button says 'start bluetooth pairing' and, when clicked, nothing seems to happen (the button reacts by momentarily shrinking to show it was clicked, so it isn't frozen, but that's it).
No 'HiFiBerry' device shows up in my available devices on my phone (LG G8 ThinQ if that helps). It isn't showing up under a different name, as enabling&disabling bluetooth in the menu doesn't have any effect on the listed available devices.
I am able to ssh into the Pi using username root and default password of hifiberry. I saw in this forum post that the command hciconfig may help diagnose the issue, but when I enter that I get no response at all.
For what it's worth, I also set up a separate installation on the Raspberry Pi 3B+ and had the exact same response, Spotify Connect works great, but bluetooth doesn't.
I'm also using a HiFiBerry DAC+ Zero if that makes any difference.