Photo size integrity

{Can export] be done with a large number of photos or does it have to be exported individually?

You can select a range of pictures by clicking on the first and then shift-click on the last one-- all the photos in between will be selected. Then Photos will say "Export Unmodified Originals for xxx Photos." Or, you can click on a photo and afterwards command-click on individual pictures to include scattered ones in your selection.

"Export IPTC as XMP"

Pictures have information about them called metadata. This can be the camera model, the creation date, the location, the title, a caption, keywords, and so on. These metadata are attached to the file in different formats and in different ways, like IPTC or Exif. Some image types and some computer systems don't recognize these add-ons, so the data can be included in a separate file with the suffix xxx.xmp. If you choose xmp, then you will have two files for every picture, not at all necessary for most systems. If you don't know what it is, you probably don't need it. If you don't need it, don't use it.

If you're using Lightroom Classic then you need to ask yourself why you're using Photos at all. Photos is a consumer level giveaway app, LRC is a pro level paid for app that is far more powerful than Photos (as it should be for the cost). Both apps are Photo Managers, both are parametric editors with non-destructive processing and both sit at exactly the same place in your workflow. Using both is like writing your novel in two different word processors. It leads to unnecessary confusion and duplication of effort.

Unless you have a burning desire to use the iCloud Photo Library I can think of no reason to use Photos at all if you use LRC.

Perhaps ASC2022 wants to do it once.

And, of course, having your phone, computer, and pad all synced together is a compelling reason for Photos, and you'd still need to get those new iPhone pictures into Lightroom somehow.

I've used Word, Pages, and Textedit for the same project...

Why would you use a photo manager once?

And, of course, having your phone, computer, and pad all synced together is a compelling reason for Photos,

You can do this with Lightroom, and the subscription means you have access to a rather greater range of controls and sharing options.

You can even take photos with Lightroom on a phone/iPad. It has an alternative camera pp, with finer control. And if you prefer to stick to Classic only then you can import images to it from any device, including phones. Again, my point here is not to criticise Photos. It's perfectly good as far as it goes. But you pay for LR and expect it to go further, and it does.

I've used Word, Pages, and Textedit for the same project...

Good, and I hope it all worked out for you. Thing is I've seen loads of people on here thinking Lrc is a pixel editor like Photoshop, and it isn't.

Image Capture is an app that comes with the Mac and is in the Applications folder. It lets you put your iPhone pictures wherever you want, skipping Photos completely. Just plug in the phone and run Image Capture. And it works for scanning and other image capturing, as well.

I don't now. I know it works for me with my iPhone 12. However, Adobe, who make Lightroom have their own forums on their site and between there and the Lightroom Queen site you'll find tons and tons of help. Also, if you are moving to LRC there are thousands of videos on YouTube and they can be very helpful too.

https://community.adobe.com/t5/lightroom-classic/ct-p/ct-lightroom-classic?page=1&sort=latest_replies&lang=all&tabid=all

https://www.lightroomqueen.com/

https://www.lightroomqueen.com/community/

File->Export->Export Unmodified

You don't even need Image Capture. Just plug the phone into your Mac and launch LRC. Then elect the import panel and it will be there as a device, like a camera.