Related question: What's people's preferred diff tool for code and directories of code on macOS? I haven't found one I liked since the Catalina update killed 32-bit apps.
Although for directories I believe it only works when combined with Git. I’ve never tried to compare 2 directories of code in a situation that wasn’t a Git changeset.
Tkdiff: instant startup, stopped working on latest update so had to junk it. Was not thoroughly happy with it because it never remembered the monitor and position from instantiation to instantiation.
Meld: Very slow startup. Takes 3s or so. Unusable from within `git difftool` due to the insane lag.
Kdiff3: Fast startup, not as quick as Tkdiff, but around 200ms or so. Currently using it happily.