Photos on Digital Camera not showing up on Computer

Are you trying to use the EOS Utility (supplied with the camera), or are you trying to use Apple software (Photos or Image Capture) to access the photos through the camera? The only place the Rebel T3i manual (as found online) suggests that you can transfer images to a computer by cable [p.285] says to do it with the EOS Utility (if you cannot read the card with a card reader).

What version of macOS are you running on your new Mac? From what I can see on the Canon support website, Canon supports EOS Utility on macOS up to Mojave (10.14.x) but maybe not yet on Catalina (10.15.x).

Have you been able to get this camera to work this way before, or is this the first time you have tried?

Some cameras have to be in a special mode to allow the computer to view the photos on the SD card (as opposed, say, to the mode that allows the computer to take new pictures or change the camera's date and time settings). Have you checked that?

If you told us what brand and model camera you are using, perhaps somebody here is familiar with that camera and can offer more specific suggestions.

Have you re-formatted the card in the camera? I have seen iPhoto and Photos get confused as to which images had been previously imported. A card format solves a lot of those issues.

If you are willing to solve this problem for a bit of money, buy an SD Adapter from Apple, this can allow you to go back to your original way of downloading photos.

Hope this helps!

Me either, but some of mine at least mentioned a download method other than Canon software in the manual, and this poster is having trouble.

sbp14, have you used this method to offload pictures from this camera previously?

What brand and model of camera?

Can Image Capture (in the Applications Folder) see the photos?

Raw of Jpegs?

And the other questions?

I have never had an issue downloading from any of my numerous Canon cameras to any of my numerous Macs without any Canon software.

One of my cameras was a T3i. 8^)

Should have led with that. :-)