I wasn't super involved, but they (the office in Ukraine) liked getting USD and people who visited would often carry an envelope with cash in it when traveling for business trips from the US to there.
There was some other thing with using US based debit cards over there, apparently it was an easier flow to fill up the US accounts and have them use it over there than to do a bank to bank transfer.
Yeah, paper currency. It was important for the bills to be crisp, otherwise they'd trade at a ~10% discount. I don't know how crypto has changed things, I don't do anything related to Ukraine anymore.
That was the same in monte negro with euros. They only accepted crisp euros even though I had brought those from an actual EU country - they wouldn’t accept them. And that was their “official” currency
There was some other thing with using US based debit cards over there, apparently it was an easier flow to fill up the US accounts and have them use it over there than to do a bank to bank transfer.