This is a field office, it handles immigration benefits cases, this is not a visa center. You'll need to be more specific with your question. But, if to assume I understood your question correctly, then no, there's no such thing as a formal invitation, unless you file for a fiancé visa, then you'll have to attach a letter of intent to marry your boyfriend once he arrives to the US. Otherwise, it would be a visitor visa for him, no need for any special letters. He will need to be honest about his reasons for entering the US though.
They work as usual. Just take longer to process applications and changed some of the procedures to account for social distancing and so on.
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