Have an older version of photo on an external hard drive. How can I import into the newest version that is on this Mac?

What is it you have on the hard drive? Is it the old photos app? Or the old photos library?

If it is the app it is no good to you - the app doesn't hold the photos.

If it is the library, you need to copy it to your pictures folder, then open it with photos (double click it when photos is closed, or open photos with the option key and select it) Photos will then upgrade the library. Keep the copy on the hard drive untouched until you have confirmed everything has transferred correctly.

What version of iPhoto created the older iPhoto library that you have? If it was iPhoto 7 or earlier you'll have to download and run the iPhoto Library Upgrader 1.1. However, that upgrader is a 32 bit app and won't run on Catalina or later systems.

If it's iPhoto 8 or later you should be able to open it with the current Photos app and convert it to a Photos Library. To merge the older library into your current working library I recommend the paid version of PowerPhotos . It can merge one library into another while including the albums, keywords, titles, captions. Projects are only copied over as albums as themes changed between versions.

Another method with Monterey is to use Photos to merge the two libraries according to this Apple document: Import photos from another library in Photos on Mac - Apple Support. However, this method does not include metadata, albums/folders or edited versions and other organizational efforts. However, it's free. All it imports is the original version.