I have a similar problem with AirPods Pro connection.
I am able to select the AirPods though - Audio Setup>Playback device - and work just fine as long as I don’t disconnect… this means not removing the device from my ears, walking away beyond Bluetooth range or answering a phone call. If I should remove an AirPod - to speak to someone or answer the phone - then the connection is broken with Audacity and I must save all my open windows and reboot the program to re-establish a Bluetooth connection with Audacity. All my other programs with audio connections (iTunes, Apple TV, YouTube, Sibelius) are unaffected so it seems to be a problem with Audacity.
My book is 438 pages long. I didn’t do anything differently with the last page except try to decrease the size of the Audacity part of the screen so that I could read the final paragraph in Preview.
I don’t have a blue tooth. I just have earbuds, and I didn’t do anything differently with them.