Managing original files after Importing Photos

I have imported thousands of photos into my photo library from my external storage which has all my images captured over the years.

After import I've let the original files stay on my external storage i.e I've not deleted them. I keep them mainly because those are all important memories and I cannot trust my Photo library solely and I need my original unmodified images for decades to come. I have also read the same here in this community and other online tutorials that its a good practice to keep the original files even after import just in case.

But now it has become hard to manage photos especially deleting photos as when I delete a photo from my photo library using my Photos app on Mac, it won't delete that file from my external storage (which is obvious).

If I find a few photos while browsing my photo library that must be deleted, then after deleting them from the photo library I have to manually check for their file names and then I've to locate & delete them using finder from my external storage as well one at a time.

What adds to the pain is finding file names of deleted photos in Photos app is hard. I have to use Get Info dialog for each deleted photo as Photos doesn't show file names for deleted photos otherwise.

So all this has made it hard for me to delete photos that I don't want from both the places.

Is there any solution to delete the photos easily from both the places? Or any way to easily locate the deleted photos in my external storage so that I can delete them? or at-least any way that makes it easier to see file names of deleted photos in Photos app?

Any simpler approach of managing photos that you can suggest will be helpful here.