This solution has set me on the right path. But there's an additional, subtle requirement to it that was needed, at least for me.
Hitting the "Cancel" button at exactly the right time was the key.
After a couple of tries, I figured the sequence :
1- click Import
2- the dialog pops-up; initially the number of photos detected is 0
3- the dialog says 1 photo detected
4- then the dialog says X random number of photos detected (sometimes 200, sometimes another number, it varies)
5- then the dialog says Y random number, which is the max it will show before freezing
6- the app freezes
I had to hit Cancel after Step #3, but before Step #4. Exactly at that precise moment, and not just before the max number is shown.
It goes quick, so you have to be ready.
If you don't catch it on the first try, proceed as follows :
- the app will freeze, just close it
- unplug the phone
- launch the Photos app
- plug the phone back
- Import again, you might need to wait a few seconds for the phone to be detected
I found that, after a failed attempt where I missed the proper timing for hitting the Cancel button, if I just went ahead and tried to import again right away it would juste freeze, every time. Unplugging and plugging the phone back again, as described above,
seems to "reset" something within the Photos app import process, that allows you to try the Cancel trick again.
So after successfully hitting the Cancel button at the right moment, I clicked on Import again and boom I finally got the photo selection dialog!
Also, the importing dialog doesn't freeze anymore !
I deleted the imported pictures and re-imported them all again in one pass with no freeze whatsoever.
Sorry I don't know if it fixes the app for all other devices one would try to import on the same machine, or if it fixes it only for the specific device that you do the Cancel button trick on... I don't have any other device to try.
I hope this helps someone else here!