Apple MacBook Air 13-inch Bluetooth is missing, will not pair or disconnects

The checks in more detail

When the quality of the sound is poor in calls, that is the Bluetooth hands-free profile at low quality, and using the Mac's microphone for input improves it. The Air's two Thunderbolt ports sit on the left, close to the Bluetooth antenna area, so a hub or a USB 3 drive plugged in there can emit noise at 2.4 GHz that disturbs the radio. Unplug it to test, or move the device to the MagSafe side. If you use a mouse that lags, check its battery, since a weak battery shows as stutter. Reset a Magic accessory by switching it off and on.

Remove devices you no longer use from the Bluetooth list. Restart the Mac and update macOS. If Bluetooth shows Not Available, shut down for thirty seconds and start again; if it persists, Apple Support should check. A Mac that connects to a device but loses it in another room is out of range: Bluetooth reaches about ten meters in open air and less through walls. If you have an Apple Watch, an iPhone and AirPods, remember that the devices share your Apple Account and AirPods hop between them with automatic switching. When you want the Mac to keep the AirPods, choose them in the Bluetooth menu in the menu bar or in Sound settings,

and set Connect to This Mac to When Last Connected to This Mac in the AirPods' settings. This stops them wandering away when your iPhone plays a notification sound. It is worth testing with a second, different Bluetooth device, such as a speaker, to see whether the problem is the Mac or the first accessory. If a speaker connects and holds a steady link at the same distance where the first accessory drops, the Mac's radio is fine and the accessory, its battery or its firmware is the cause. Note the distance and the room so that support can see the pattern if you contact them.