Don’t know if yogurt/Greek-yogurt still contains milk sugar, i.e., lactose, after processing. If it does, our veterinarian says not to feed it to the domesticus felinus - gives them the runs, which is unhealthy.
Yogurt in small amounts is OK for cats. I asked my vet and it said that, being fermented, it is digestible even by people lactose-intolerant. What my cat gets is probably half a teaspoon x time, not overdoing it. It is the plain kind as all artificial sweeteners are not good for them (or people). Anyway, thank you for your warning.