AirDrop issue with KML/GPX file from iMac to iPhone: iOS demanding an app from App Store

AirDropping KML files from iMac (27" 2019 - 11.2.1) to iPhone (8 - 14.4) is no longer working (completely).

It was all working flawlessly as recently as a couple of month ago (possibly even more recently).

Background

On iMac I have BBEdit set as the default program to open KML and GPX files (as I edit them frequently).

On iPhone I use several apps for these type of files but usually Maps.Me for KML and WorkOutDoors for GPX (to send to Watch (5 - 7.3).

Symptoms

The AirDrop process works up to the point of accepting the file in iPhone.

In the past iOS asked which of several apps I wanted to open with the most recently used one at the top of the list. Aside from a number of useless entries in the list (No, I do not want to open a KML in Overcast or Contacts) this was all well and good.

However when I did this yesterday iOS said "<My Name> would like to share a file that requires an app from the App Store". The choices were "App Store, Open with Files and Decline". The App store route takes one nowhere. Decline does work.

Workaround

The Workaround is simply to open the file from the Files app using Share. The Share tab has all the appropriate (and some worthless) suggestions for apps with which to open the file, and the process works as it should. However the files do need to be in iCloud to appear seamlessly on both devices, and I sometimes prefer to AirDrop directly from the iMac's local Download folder.

Tests

I tested the same file (it's stored on iCloud) sent from my MacBook Air and the result was the same.

I then sent the file to a friend's new MacBook (M1 - 11.2.1) which had never previously had a KML on it. Then from this MacBook I was able to AirDrop the file to both my iPhone and her iPhone (11 Pro - 14.4).

In the first test the KML file immediately opened in Maps.Me on the iPhone 11 Pro with no question. On the iPhone 8 it did ask which of several apps I wanted to use, which is the expected behaviour.

After installing Google Earth app on the iPhone 11 Pro it then asked which app we wanted to use (Google Earth, Maps.Me or Open with Files).

Conclusion

I am not sure where the problem lies:

• Either in iOS for erroneously failing to identify the file as a KML (despite the filename suffix, and the fact that MacOS identifies it as a Google Earth file, and the fact that the iOS Share tab knows correctly what to do with it).
• Or in the iMac which has a default program set which evidently is not in iOS (as its a programmer's editor). I have tried setting the default to Garmin Basecamp (which it had been some time ago) and also removing all default programs for KML/GPX files so that "Open with" defaults to TextEdit. This made no difference.

The icon shown on the iOS AirDrop acceptance screen is the BBEdit icon with KML written underneath. When the default was changed to Basecamp on iMac this iOS screen icon also changed, so it is appears to be coming from the iMac. Obviously neither BBEdit nor Basecamp are installed on the iPhone.

I conclude that iOS is receiving from my iMac some metadata about the file which leads it to think that it needs an app that it does not have. From the M1 MacBook it is somehow not receiving the same metadata and thus it open in the appropriate iOS.

So the questions is

How to proceed to get back to the status quo ante? Do I have to patiently wait for iOS (or MacOS) to be fixed.

I do not believe that this is limited to KML and GPX files. I presume it could apply to any file type for which there isn't necessarily a native iOS app. One further note: PDF and image files transfer as before, but then I have not changed the default program for these on iMac.

I am wondering if there is an app on iMac with which I could associate these two file types that would trigger its acceptance on iOS as a "mapping program" type file. I would lose the ability to just double-click my way into the editor, but that might be a price I would be prepared to pay (temporarily) to have AirDrop working again. As noted above, associating it with Basecamp did not do the trick.

Any suggestions gratefully received. Thanks.