Yes, the IOBluetoothFamily attached is already patched with dokterdok method, and 
@ASentientBot is right, I made a typo.
The syntax correct is 
sudo kextcache -i /
Retry and it should work.
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Maybe is the battery in service mode or replace now mode?
		
 
The -i definitely had the command doing something for a while.  Unfortunately, I’m still in the exact same boat, there is no change.   I really don’t know what I’m doing wrong.
45 minutes later...
Ok, I found part of the problem...
As far as I have seen, it should automatically switch over to using the Bluetooth 4.0 dongle.  You did mention in your first reply about the light on the dongle flashing, I think.  But it has never flashed, it’s always been a steady blue.  So I went searching.
I just looked at System Information.  It’s never switched over to the dongle.  First, it says it doesn’t support Bluetooth low energy, and second, I paired my AirPods to the Mac and then pulled the dongle out... the connection never died or hiccuped.  So for some reason it has never switched away from the built-in Bluetooth.
I tinkered and tinkered, and finally upon switching Bluetooth off, waiting 6 seconds, pulling the dongle out, waiting 6 seconds, plugging the dongle in, waiting 6 more seconds, and turning Bluetooth back on, it finally switched over to the dongle.  Different MAC address, and system information now shows supporting Bluetooth low energy.
However, I have no idea if I’m going to have to do that every time I boot.  I did reboot and it stayed on the dongle (I made a note of the last 2 digits of the MAC address of both to more easily tell the difference in the future).
AirDrop is now working perfectly.  I can see both the iPad and the iPod from the Mac.  As soon as I tap the screen to bring the screen to life, they instantly appear in AirDrop.  And I can finally see the Mac from the iPad and the iPhone.
So good news there.
However, the bad news is the rest of it is wonky.  I get instant hot spot on my iPhone along with what I have had, messages, phone, and now AirDrop... but no more.  However, the iPad is a different story.  Universal Clipboard, handoff, and Continuity Camera are working.   Sidecar, sketch, markup, and instant hotspot are not (though it’s a WiFi only model, so I’m assuming it’s not suppose to have instant hotspot).    Pay is unknown.  I don’t need to buy anything at the moment.
i don’t understand why the iPad is working more than the phone.  It’s a first generation iPad Pro.  The phone is the newest one this year.
But the end result is much better than before.  Hopefully I can figure out the rest tomorrow.  Maybe you’ll have some ideas?  Hopefully the dongle keeps working and it doesn’t default back to the built-in.