Interestingly, plugging the same phones into my old Macbook running 'Mojave', the previous release, gave a non-functional Android File Transfer, backing up the theory that something's changed under the hood in Catalina to somehow improve MTP access. And, over the last 48 hours, I've been plugging in various Lumias over Type C and microUSB and all have worked. Without any real hope I clicked on a reported folder in the phone and was astounded to see that I now had full access.

I plugged in my Lumia 950 XL into my Mac to give it a top up charge (my Qi pads already being occupied on my desk) and saw AFT kick into gear as usual.

This changes with the latest Mac OS release, though. Up until Mac OS Catalina, if you plugged in a Lumia to a Mac then AFT (if installed) launched but clicking on any of the reported folders in the phone just popped up an error. 'But wait', I hear your mind click into gear, 'if Android File Transfer (AFT) adds MTP to the Mac then surely it will also work with Windows phones?' In theory, yes, though it hasn't until now. It's a little glitchy (you sometimes need to plug in a couple of times) but it works on the whole. So you typically plug in your Samsung Galaxy or Pixel or similar, set the USB mode on the phone and then you're away, dragging and dropping media/documents in both directions, phone to Mac and back again. On an Apple Mac, things are different in that there's no native MTP support (again, the protocol is a Microsoft-invented thing) so you have to install a small Google utility, Android File Transfer (AFT), and this runs with a drag and drop interface for anything you have connected. On a Windows PC, this is usually enough to have the Android phone appear in Windows Explorer and you're away. That done, these Android phones then also present a MTP interface. In the parallel world of Android phones, most of these default to 'charging only' when you plug them into a desktop of any kind - and there's an onus on the user to swipe down and then change the USB mode to 'Transfer files'. And it's worked perfectly with Windows on both ends for a decade, not surprising since MTP itself was a Microsoft invention in the first place! The idea being that the desktop (a Windows PC is the intention) then mounts the phone in its file system for the purposes of dragging and dropping media files/documents to the phone or from the phone. Windows phone devices (of any era) present a MTP (Media Transport/Transfer Protocol) interface to any connected desktop.

Now, I've known the theory behind this for ages.

Mac os file explorer for windows