getting data from a 12 year old backup

The Finder can do an 'All images" search on a disk or folder but I'm not sure that will be the assistance you think. An iPhoto Library contained multiple versions of the same photograph - The original, the preview (if edited) and several thumbnails. So a simple search will find thousands upon thousands of apparent duplicates. They won't be duplicates, of course, because they're all different sizes, but you'll be doing a lot of work to get the original images out of that lot.

Further, that process destroys data - basically any work you've ever put into those images and/or those libraries will be lost and you'll be back to square one.

A more effective search would be to look for folders called 'Originals' or 'Masters' (the name of the folder changed in different versions) and see if you get to those. Again, this would be destructive but if your content to start over the app FindAnyFile will also search for folders...

https://findanyfile.app/

I would not trust anything Chat GPT suggests. You've already correctly questioned its results so you also don't trust its suggestion....good for you! Most things you find on the Internet tend to be wrong anyway and it requires a person to question everything & try to understand the suggestions to see if it may be useful & then try to figure out how best to implement it. Many suggestions are poorly implemented, but there may sometimes be a small nugget that can give you a clue on possible options.

I don't know how you backed up these various systems or how those backups are configured for accessing data. If it is a Time Machine backup, then you should be able to Option-click the Time Machine icon on the menubar to "Browse other backups" to pull data from them.

Unless you are a programmer who can write some code to access & parse the various backups looking for items (probably a big order even for an experienced programmer), then you will need to resort to slow manual brute force of attempting to access the backups or hope the older systems can hold up to transferring large amounts of data.

The ChatGPT suggestions look very incorrect to me. I would not follow them.

As HWTech noted, you can try browsing the Time Machine backups, but that could be laborious. But in principle it should work.

Here is another approach: obtain one high quality new external drive for each older computer that you want to recover files from. Make a "clone" of each computer to one of the external drives using SuperDuper or CCC or another equivalent tool. I think SuperDuper has a free demo version that will do this.

Once you have those "clones," you can then find all the image files and iPhoto and Photos Libraries on each, and open each Library on a newer more reliable Mac to assess what is there.

If all you want are the image files themselves, you can access those on the iPhoto or Photos Libraries by right clicking on the Library: select Show Package Contents and look for a large folder called "Originals" or "Masters." That large folder will have the actual images files. You can COPY (not MOVE) them to somewhere else safe. Then you can do what you want with them, including importing them into a new Photos Library.