On Windows, WinMerge[1] is a better alternative. Too bad is Windows only.
For a non-FOSS and cross platform solution I recommend BeyondCompare (U$30.00)[2]. It replicates most of WinMerge UI.
P4Merge is very good at the second but not so much at the first.
Also, to this date it doesn't have an OS-X version for M1 CPUs.
My SO adores Meld, but she works with Linux. I tried using it but couldn't get used to it. She also makes fun of me (half in jest) because I use Tortoise Git instead of the command line...
Back before git, it was common to take a massive set of changes and merge them manually when merging branches, and BC was the only tool that made it painless for me.
I stumped up my own cash for a pro license and I use it almost daily even now.
Update: I just downloaded Meld. It literally takes ~half a second to change the cursor location when I click in a highlighted region, which is already making me dislike it. Is this normal?
It means you can do things like compare two system logs from different times and have it highlight you exactly the differences you care about.
Pro version gives you 3 panel merging. If you use that a lot then it might be worth it. Or, instead, use P4Merge for it.
The other thing is that the trial used to be very fair. I don’t know if they changed it, but it used to give you “days of usage” not contiguous days. I once used it for about 5 months because the 30 day trial only counted the days I actually used it and I saved using it for when I really needed it, and used WinMerge when I could instead.
Beyond Compare is a gem.