Best apps for removing duplicate images in Photos?

I discovered rather late that the current version of Photos under Catalina always exports files with a .jpeg extension, even if it was originally .jpg — which is the one most cameras and smart phones seem to use. What's more, when importing it treats the .jpg and .jpeg versions as separate images, so they are not caught by the 'already imported' filter. You can get around this by changing the extensions to .jpeg before importing.

However, I now have 6,000 duplicate images to get rid of. I would like to know of other users' experiences with apps that do that. I installed 'Duplicate Photos Fixer' from the app store on a trial basis and it seems to work, though you have to mark each deletion individally, then go into Photos to actually delete them. On the other hand, I have had problems with Photos since using it (separate posting), so have to wonder if this program was the cause? I would prefer a program that was semi-automatic, i.e. just deleted identical copies of photos that meet criteria I can specify.