This is something I’ve seen mentioned a number of times on this forum and think would be really, really useful.
I think Monzo’s response has previously been something along the lines of “it would make stuff overcomplicated for users” (I could be misremembering though!). This argument doesn’t make sense to me because the ‘split into multiple categories’ option could be easily placed as the last category option when you go to change a transaction.
Integration with Amazon/supermarkets etc… (like you suggest) in the future would be great.