In spoken English, in US custom, you could just say "noted." This is neutral in tone. In a meeting, if someone is talking to you and being insistent and repetitive, sometimes people say "I hear you." This is informal. It means "I don't agree with you completely but I did pay attention and understand what you said."

Affirmative. Right. Right then. OK (with the right tone). Most possible ways to say this sound less formal than "duly noted."

So, in order of formality (as far as I can say as a British English speaker); Duly noted/ I'll take it into consideration Noted Check Absolutely Sure thing/ righto I'm certain there are more. But these cover most situations!

Lots of ways to say this. I understand. Understood. Got it. Check. Of course, some English speakers love irony, so (with friends) you can say things like even though you might be in complete agreement with the person (which should be clear from the context and your relationship, otherwise you might get into trouble!) Really? As if! You must be kidding! I hope that is helpful.

‘Duly noted’ isn’t just formal. It has a different meaning than most of the other suggestions. It means ‘I’ve written this down as I’m required to do’ ‘Noted’ by itself is a little less formal and could suggest the same meaning. The idea that what I’ve done is required would be understood without being said. And there are probably people who use ‘duly noted’ to intentionally sound more formal even though the meaning is different. They shouldn’t unless they are saying it to be humorous or sarcastic.