What makes the harmonies in "Don't Know How to Keep Loving You" by Julia Jacklin so layered?

The chorus stacks multiple takes of her voice — a high, thin falsetto over a fuller chest voice, plus a low harmony that barely moves — sounding like three versions of her arguing. The bridge layers a descending melody against the main line, with a third part echoing the last word of each phrase. For the best example, put on headphones and focus on the end of the second verse, where her voice splits into three distinct paths right before the chorus.