I've been a passionate Beyond Compare user for about 2 decades now. I swear by it. Great for diffing images as well.

I'll have to check it out, but I'm pretty happy with Kaleidoscope. https://kaleidoscope.app

Adding another vote for BeyondCompare. It's not free, but it's fantastic.

I use Beyond Compare mainly for sync of folders by comparing files (sizes, dates) and not for file contents diff as such. Part of my backup strategy while copying/syncing file between windows/mac/NAS ;-)

Another vote for Beyond Compare here, 10 years service with Git.

Does BC has 3 way diff/merge?