I think you’d be very surprised at how much lawyers don’t know or care about any of that. They store stuff in the cloud without ever having heard of the Third Party Doctrine (which allows the US government warrantless access to those documents).

They do. Most of them use proprietary https web interfaces that usually have "secure email" or "secure messaging" in the description but they are just fancy web portals. I despise those systems. The content is not encrypted at rest and can be leaked. With OpenGPG the emails are only decrypted on the recipients end points and can be deleted by request.

Not all of them. I keep seeing lawyers sending photos of sensitive documents using their cellphone and Whatsapp (before encryption), and most of them don't even care about all those documents still residing on their cellphone, at the mercy of whoever steals it since all the security they have in place is that swipe thing that anyone with good eyes spots in 2 seconds straight.