https://www.airwindows.com/deess-vst/
The Airwindows DeEss works by tracking slew rates, not by filtering and frequencies. It keeps a string of recent slew rates, and if it sees high slews that keep going back and forth (flipping direction) that’s how it triggers. It doesn’t trigger on things like square wave or sawtooth waves, because those aren’t going back and forth fast enough to be an ess. It’s purely mechanical: the trigger for DeEss happens instantly and way more powerfully on real esses, making it extremely easy to set. It’s not fiddly, just crank up the effect so you can plainly hear where it hits and use that (don’t overtrigger, for the bad esses you’ll get a HUGE powerful trigger even when everything else is totally clear of de-essing)