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You don't have to be a suited and booted - of you are a guy I would wear a collared shirt - but no need for a tie/jacket. In some ways women have it a lot easier as there's a lot of things they could wear that would look smart on camera. As long as your shoulders are covered and it isn't too low cut, you’ll generally be fine. I wear a t-shirt and cardigan most days on zoom and it looks smart where people can only see my neck and shoulders