Your accounts and balances come over. Each YNAB category becomes an envelope in the same group, with the money in it, including money assigned to later months and set aside for card payments. Hidden ones with money go in a hidden group, and empty hidden ones are left out. Ready to Assign should match YNAB’s.Targets and scheduled transactions stay in YNAB. An overspent YNAB envelope starts at zero, and Ready to Assign is that much lower.
Export right before you switch. From then on, log new spending in Bow, so nothing is missed or counted twice.