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As a rule of thumb, if you're legally resident in a country, you can apply for the visa there. So you can apply in Dubai/UAE.
Since the B1/B2 visa is a "non-immigrant" visa, it cannot be renewed or extended, you need to apply for a new one. To apply, you need to have a specific tourism or business reason. So I would not recommended applying for it again until you have a reason to travel and some documentation to back it up.
Getting a 2nd visa is usually much easier than the 1st one, because you already have legitimate travel history. There is no problem with a gap of a few years, particularly now with COVID, since a lot of frequent travellers are effectively grounded anyway.