Frustration due to inability of iPhone and iMac and iPhone and PC not able to talk to each other so I could transfer photos from iphone

I am coming to this community as few of the last resorts.

My iPhone is getting full. I have to transfer the photos and videos from iPhone to computer. A simple task. But has become a major undertaking with no success so far.

Apple Software does not give enough feedback to user. I connect my iPhone to iMac. Sometimes it shows up in Photos and sometimes it doesnt. When it doesnt, I am left high and dry with no message either on the Mac or on the iPhone as to what happened. I have to restart the iMac or iPhone or both to get things going. Only for couple of photos - and then it stops. In error scenarios I hear a beep.

I turn to PC. Same thing. Except I get an error message "Something went wrong" - which is very obvious to me :)

Has anyone experienced this issue before? I have a feeling that I am missing something important and I cant figure out what. Any advice?