So the only person we can find who claims to have used BTC to flee Ukraine is a guy who is literally the webmsater for a company that raises money to mine crytpo. And he didn't buy BTC when he wanted to flee Ukraine, because he couldn't because the banks had stopped withdrawals, he took the BTC he already had saved. And as the article notes - since he has bitcoin, he didn't need an ATM he just sold it to people he knew in Poland for cash. And that's all taking it on face value that the story isn't just straight BS.

Personally, if I were living in a place that is at threat of war (and let's face it, this war was no big surprise) I think I'd be much more likely to just keep a few hundred dollars stashed away in cash, than rely on a usb stick.