An update: I did a "Reset Network" and a "Reset All Settings" (annoying - tried to do a backup/restore, and then the restore failed with multiple tries so I had to manually put all the settings back). The BT connections to my Fitbit Charge 3 and Garmin Forerunner are working and steady, but not to the Plantronics PLT M165 which keeps dropping. However, if I connect the M165 and play a music playlist, it stays connected for the entire time (I listened to music several times, once more than an hour). I concluded that there is some sort of timeout that is occurring that is activity-based. If it is connected and there is an active transmission going on, it stays connected. Since my Fitbit and Garmin devices stay connected without issue, I'm thinking it is PLT M165 specific. I can't say whether it is the iPhone 11 or the M165 that is terminating the connection. I've emailed Plantronics support, will report what if anything they say. I may end up buying another brand of BT headset and see if the issue follows. Too bad because I like the M165.