DnD above table and meta gamers

So for context I’m curious how much DMs allow above the table talking infront of NPCs particularly if the PCs are having a conversation with a NPC then start chatting among themselves without saying we whisper or step outside.. do you as DM react as if NPC hears them ? Do you then ask them if they are saying things in character?

Also when two PC are not within talking range but are giving eachother advise on what they would do — do u just sit back and let them or say something like,” you hear the voice of your companion in your head heading you to do xyz, knowing it’s what they would expect of you.. now what do you do?”

I’m ok with some tweeting between PCs but I do feel like there should be a limit ..

I also had a player tell me he could only meta game.. if he as Player knows something then his character now knows said thing and he will
Act on it accordingly.. he said it’s impossible for him to not use the knowledge he has if he has it ..