This has been an issue at my table, to the point arguments have broken out, and I've been having a rough time finding an answer to it online:

Is it okay to whisper to one another while someone else is talking, or during someone else's turn in combat? And does it make a difference if it's in-character or out-of-character?

Out-of-character example being, typically, about the game itself. Things like asking questions about how something works in 5e, or questions like "do you have anything planned for your turn? Because I can do ___ if you need me to"

When it's in character, does it matter the importance of it? For context, some examples of things whispered include: "we were discussing what we'll buy in-town together" and "we're both wizards and are discussing what spells we're both preparing for today."

What if it's spoken in-character, but in a language besides common social etiquette? Meaning that only those whispering are the ones who would understand it? Is it better to just have those conversations openly, or via written notes/DMs, or just avoided at all costs?

All I can find on "talking during other people's turns" is people talking over one another and being loud, I can't find anything about whispering quietly to one another. I'm interested in some clear answers from experienced people, and if there are any caveats, etc.

I don't know if I want to bring