Iphoto not supported on new MAC PRO?

iPhoto was discontinued 6 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.

iPhoto needs some system libraries, that contain 32 bit code and are no longer included in the newer system versions, that are strictly 64bit since macOS 10.15 Catalina or later.

Apple has replaced iPhoto by Photos for Mac in 2015, when Apple stopped the development of iPhoto. Since then the new Macs are coming with Photos as a part of the system. You can convert the iPhoto Libraries to Photos Libraries by launching Photos while holding down the options key ⌥ while clicking Photos. Then select the iPhoto Library you want to open in Photos. You will find all photos and iPhoto albums in the new Photos Library, including the adjustments and most metadata.

See: https://web.archive.org/web/20200315041706/https://support.apple.com/en-us/HT204655

I have the same issue, except I exported my iPhoto library to an external hard drive before my old MacBook Pro gave out after 9 years. I didn't know that iPhoto had gone away, or that my new MacBook Air wouldn't open it. With my old MacBook it'd ask me which library I wanted to open.

I plugged the hard drive into my MacBook Air and it doesn't recognize anything. I can see tiles when looking at the external drive, but none of the file organization. Just thousands of little squares.

Since my photos aren't on a Mac, I can't migrate to Photos and keep any info. Can't even sort by date.

Any suggestions?

Basically: same problem then same solution. In fact it's the only solution.

I'm afraid this isn't clear:

I plugged the hard drive into my MacBook Air and it doesn't recognize anything. I can see tiles when looking at the external drive,

What does "doesn't recognise anything mean"? What are "tiles"?

The fact that your library is on an external disk doesn't matter - as long as the disk is formatted Mac OS Extended (Journaled) or apfs.