Yeah. Wearing ridiculous outfits that highlight they almost ridiculous bodies, to make sure the player knows that while she is not a 18 years old, she is still hot as fuck!, going all "I will suck my baby cock to help him with his pain, come baby, cum for mommy"... sorry.. I think I just vomit a little inside my mouth
Alexandra in Amnesia is a great Milf for example. She loves the main player, hugs him and kiss him, but always projecting this impressive elegance, this pressure on the MC.
Emily in Intertwined, while not a LI, is also a totally milf if I could I would go full incest on her. Best girl among all girls in that game.
Cordia, while not MC mother, is the pinnacle of a Milf done right. Although, if instead of her age we would say she is 30 it would work too.