How would i stop the ability to push npcs like how players are resistant to push?

i want players to physically collide with npcs, whilist not pushing them like they weigh nothing. i dont know how to achieve this though, i saw an old devforum post made by roblox staff saying something along the lines of “player characters’ are treated as infintely massive” which was in response to somebody saying they had the ability to push other player characters n its a security issue.

i dont know hhow i wuld do that or if its irrelevant?