Exporting photos from Photos, macOS

It's not. It's perfectly possible. If you are having an issue then you'll need to tell us what that issue is in more detail: what version of Photos, how you're trying to export, where it fails and what error messages you get, if any. Also can you view these images full size in Photos, and any other details you may think helpful. After all, we can't see your machine, so we need you to give us the information to assist you.

Your library is in the Pictures folder, right? Have you tried repairing the library by launching it with the Option+Command keys held down?

What happened when you try to break up the export into smaller groups?

Download and run Etrecheck. Be sure to give it Full Disk access before running.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can evaluate the report to see if we can determine the cause of the problem.

I don't see any of the usual suspects in the report. You are behind in your Time Machine backups. You should make a new one right away.

Also the battery may be at the end of its cycle. The report says it needs service. You can download and run the free app CoconutBattery to get an idea of the battery's condition.

Can you export as Jpeg? Where. are you exporting to?

So you can export single photos as Jpeg? Or as PNG? your response is not clear.