Importing photos from iPhone/iPad to Mac

My stuff is all in French, so sorry if I don't give the proper translations of option names.

I try to save all the photos from my iPhone and iPad to my Mac for back up. I go in the Picture app and I go into import after plugging the device. I see the device in the left menu. I open it. It says that I have 82 pictures not imported yet. Fine. But I know that there are hundreds of photos in the device, I can see them when I look in the picture app of the iPad itself. I want a full backup. The other pics have not been imported into this Mac. They might have been copied in my old PC a little while ago, but I did lost many things when it died so I would like to be sure having a full backup, and later I'll be able to delete any double. How can I do that ? Now that I imported the 82 photos, it just says that the iPad contains 82 already imported photos and no mention of the rest that is on it.

And if you have an advice on the format I should choose when I export those files to keep them in an external backup, I would be very grateful. I'm not a professional photographer. It's mostly family pictures, memories and a bit of stuff I use for work and social medias. If I ever print, it's to make a souvenir photo book, not a wall-large professional print lol. I guess that JPEG would be sufficient because the lack of quality is probable under what I can even notice and the space saving would be worth it, but I'm afraid of making an error.

Thank you for any help provided. I'm still new to Mac and I don't get all of it yet.