Maybe I'm outside the norm, but as a YNAB user of over 10 years, I've never needed this. We split transactions across multiple categories all the time (shopping at Target for groceries, clothing, household goods, etc), but I expect that is very common.

I don't think YNAB philosophy would have you tracking reward or gift card balances, so you'd only track the amount that hit your CC, in this example. In that regard, YNAB certainly isn't a tool to track all of your monetary assets.

Is it common to split a single transaction across multiple accounts?