You can "conceal" a full frame handgun by standing like a robot and not moving at all, but I've found often that all falls apart when you start moving at all. In winter you might get away with it with how thick all the clothing is, but every other season is no go.
A Shield is the absolute largest I would use for carrying, and the LCP is probably the smallest I feel comfortable shooting.
The Suited Shootist on YouTube is a small channel but I find he has good advice for people that want to conceal their firearms, not "conceal" them.
Just to clarify, my definition of concealement is being able to do daily activities in different positions without giving yourself away to someone observing you.
I don't feel the need to carry a full-size because any situation where I'd need the extra accuracy is one I can likely run away from. Not looking to get raped by the court system and the inevitable civil lawsuit.