Airdrop on Mac isn't working

I can't get Airdrop on my Macbook to work. This has been happening for months, and I've got used to it and I had given up trying to fix it. But with the release of Big Sur and buying a new iPhone I was hoping it might fix itself, but it hasn't. I've tried every combination of restarting and settings that any of the help documents have described, but nothing has worked.

Here's what happens. My phone can see my Macbook, and my Macbook can see my phone, but when I try to send anything in either direction it either does nothing or says "Waiting ..." Nothing ever happens after that. I have it set to "Everyone" on both devices and I use my iPhone to send and receive via Airdrop all the time with other phones.

I've tried restarting, switching Airdrop on and off, I've tried turning personal hotspot off and on, I've tried turning Bluetooth on and off. I've ensured that both devices are on the same network (and tried it when this isn't the case).

The phone can also be seen by the Finder and I can even drop files into it when it's mounted in the Finder wirelessly (i.e. drop documents into doc reading software). But Airdrop just doesn't work.

Anyone have any ideas of how to go about testing / fixing this issue?