How to move photo library and referenced files to external disk, and update the reference file paths

Thank you for the reply. Ideally we would be using the scenario you describe but we are dealing with a photo repository built over the last 20 years. Hopefully some of the experienced users have been dealing with photos on Macs for that time frame and are familiar with the scenarios that existed before the Photos app.

The photos are only referenced files because of that long history, not a specific intention or need. During the 2000s the photos were loaded from digital cameras onto a Windows PC. In the late 2000s/early 2010s they were moved from PC to MC. I don't recall what the Mac program or method was used at that time but I think it was similar to the referenced files method. Sometime later they were accessed using iPhoto as referenced files. It was then retired and replaced with the Photos app and so that's how the photos came in, as referenced files for photos loaded before about 2011-2015. Anything loaded since then is not a referenced file but only stored locally in the photo library.

So the library has a mixture of referenced files and local photos, and we are now trying to get it all into Photos natively. As I thought, and as you suggest the manual option should work but doesn't. The external drive format is Mac OS Extended (Journaled), with 2 partitions, one volume for photos and the other for TimeMachine backup. It is directly connected with USB.

Unfortunately I can't do that because of the original problem, the reference files aren't found by the Photos app. As I mentioned earlier, even though I can use Photos to navigate to where the original files are and they are listed, they are ghosted and Photos can't select them. Therefore I can't relink them and they have to be linked in order to consolidate. Consolidate only works if the link to the reference file is working.