I don’t know what everyone’s tried or heard before in Diatonic.  Of course it’s important to select the matching Key & Scale, and the harmonies desired in Pitch A & Pitch B.  Stick to single-note lines and simpler double-stops.  But it’s equally important to simulate the multiple guitar overdubs.

Add up to several dozen milliseconds of delay time, with Delay A offset in time from Delay B (and also from your dry guitar).  Balance between the harmony voices with Pitch Mix.  Use an EXP pedal to slightly vary Pitch Mix to either side of center at A10+B10.  That will a little greater emphasis on one or the other ‘overdubbed’ voice.

Here’s a quick example I tossed together that may give you a head start.  Quant is OFF in Diatonic, for more forgiving string bends & wider vibrato.  The Weedwacker instance in Series is optional.  I just used it to push the midrange, and add some hair to the output.