I am not 100% sure a squat switch is needed in a glider. Here’s a quote from Garmin through an AOPA article-
For aircraft without retractable gear aircraft, Garmin ADS-B equipment analyzes various data available to the system for air/ground determination. This includes groundspeed; vertical rate; airspeed; radar altimeter, if available; a rotorcraft’s collective position, if available; comparison of aircraft altitude to nearby airport elevation, if available; and comparison of groundspeed and/or airspeed to aircraft stall speed, Garmin’s Stone said.

Trig is the preferred transponder for gliders due to size. Does anyone know if a Trig transponder analyzes data like Garmin equipment?