You might have to jump through hoops downloading it from GitHub.

And so the link leads us to which in turn has a link to which is the GitHub repo the sources are downloaded from. If anyone is wondering why the source has changed, Dupeguru's website says the maintainer has changed. Anyway, here's some explantion of the current state of affairs - these aren't my words, I think they're in a comment field on one of the sites listed in the comment. Click Scan button to start finding the duplicate files. Click + button on the bottom, and add the folder you want to scan. The old version works for me, so I'm not going to commit to the latest yet. Launch dupeGuru either from Unity Dash or Menu. Now it looks like maintenance has been picked up by someone else. The original author of dupeGuru stopped maintaining the app in 2016 which hasn't been an issue for me (except there are no help pages.) The app is pretty straight forward. Search for that, it might also be called dupeGuruME. I have no affiliation with whoever produced it it's called dupeGuru Music Edition. Surprisingly the free app that I've been using for years still works in Catalina Music.

Dupeguru cost