Photos App import fail from camera card *or* internal hard drive

Recently got a new M4 chip MBP and the Photos app has been completely unwilling to import photos from a camera card in any way that makes sense to me. Mac OS 15.4.1, Photos App 10.0 (751.0.104). The camera card is formatted by my Canon camera as ExFAT, and I've found here that Photos doesn’t like anything other than Apple formats, so I’ve stopped trying to import straight from the camera card and am copying to the internal drive, then importing to Photos.

Here are the two ways I'm trying, and what's happening with each of them:

1. drag and drop from finder window to Photos: sometimes nothing happens at all, other times the number of photos I'm dragging appears in place of the mouse cursor, but then snaps back to the finder window when I release the mouse button, but sometimes the import window opens with some of the pictures and some previews that refuse to load
2. command-shift-i from the Photos App (or menu File... Import), navigate to a folder containing the photos I want to import, select all, click Review for Import (or type Enter key): if there are only 30-40 photos, this seems to work, BUT if there are more photos, some of them either don't show up in the import window at all, or show up as blank and a preview never loads. But the most annoying thing it does is just plain not import some of them.

Like I said, the most annoying part is when it imports some of the files, but not all of them.