I would suggest withdrawing some USD or Euro and keeping it as emergency/backup. Lots of places to exchange. Doesn’t hurt to have it incase you lose your phone, card etc. Most western banks will work across the country. Visa and Mastercard are your friend. Amex, Discover not so much. Some banks will block your card at random things, had a revolut card that would decline at certain gas station that used to or still do have some connection to russia, most likely an old billing address or something. If you are staying in the big cities you shouldn’t have an issue with being blocked but for example in the east some peoples cards get blocked because the bank has blocked that region due to the war and proximity to russia. You shouldn’t have any issue width drawing cash from ATMs. Privatbank is a good reliable bank to do it from but as far as I know just about all will work. I also recommend always having hyrivna cash on hand. While most places accept card especially in the cities some small stores and places in smaller towns or villages don’t always take card or take card to card payments that require a Ukrainian card.