Where do you draw the line as to what is or is not cultural appropriation?

In fact, AFAICT, the Ashkenazi custom of plaiting a special loaf of “Sabbath bread” was adopted by European Jews from Christian communities that braided bread for Sundays, starting in the 15th century or so.

Every custom everywhere, pretty much, was at some point borrowed or modified based on other people’s customary practices. That doesn’t mean that the concept of “cultural appropriation” has no meaning whatsoever, but it does mean that it’s impossible to define it precisely or make one-size-fits-all rules about it.