macOS Catalina mail sending .heic format instead of .jpg

After an update to Big Sur, this issue seems to be no longer present. I have sent only couple of emails with photos in them, but so far, every one of them has been automatically converted and (alternatively) resized. I'm hopeful it might be ok now.

Thanks. But that's not the point. This looks like a bug to me.

Just few moments ago, I sent an email to friend of mine. I attached multiple images from Photos on Mac. I took them all by my iPhone 11 just recently. MacOS Mail converted them all but one. See the picture:

I become used to that I can send anything I want from Mail without the need to convert anything. It's a wonderful feature I like a lot. No more separate exports for mail, just drag and drop and set up the target resolution.

It started to fail, though.

The same here. Haven't tried under Big Sur, though. Meanwhile, I used a workaround: click on picture in photos, hit cmd+C and then cmd+V in Mail. The picture is pasted properly, although in smaller resolution, which is no problem most of the time.