In a Switch* you don’t “need” a Ground wire, but you will need a Hot and a Neutral wire.
The Hot brings in current from the grid. Don’t touch the hot wire, cuz even if you’re not grounded you usually get a shock (perhaps a very bad one).
The Neutral returns current back to the grid. You might find one carrying current already because it is on it’s way back from something else in the circuit. Regardless a “smart switch” needs a way to grab current, so it flows from the hot to the neutral.
The Ground returns current back to the “earth” in the rare case that there is an electrical fault (i.e., a short) and the switch or toaster, etc., leaks current to some metal part of the appliance. Appliances usually tie all their metal to the Ground so that it will “spill” the current to the earth instead of the human touching the toaster or vacuum’s stick or fridge door or …
A circuit can live without a Ground, and switches, often don’t have grounds because they aren’t like appliances, etc.-- they don’t have exposed metal parts. Old home “two prong” outlets also don’t have Ground wires, but may ground the wall box itself.
A smart switch can be powered between the Hot and Ground, but that is a “no no no” because now the ground line will carry current all the time and could shock anyone on the circuit touching metal of an appliance; more than defeating its purpose.
So … are you missing Ground or missing Neutral?
In a Switch you have: Hot In -> Switch -> Hot Out
That’s all a dumb Switch requires to operate.
A Smart Switch (except for Lutron) requires Hot In -> Switch -> Neutral Out and Hot Out.