5 stars for being one of a kind, for many years I used Total Commander (TC) on Windows, but to my surprise I found no GNU/Linux equivalent to TC's "Synchronize Directories" function (in particular they don't delete files on the remote part). I regularly use Double Commander but neither Gnome Commander nor Krusader have such a comprehensive feature as TC. However the modest and small DirDiff does it very well and also up to 5 different folders! I'm using LinuxMint 19.3 Mate at home and LinuxMint 20.2 Mate at the office, you have to create a DirDiff launcher on the desktop because it doesn't register in the menu, but you have to run it from the terminal.
Needs to be launched from the command line, and hasn't been updated for years... But it still works and is the best GUI tool I have found so far for comparing similar folder structures like originals with backups.