Thanks for sharing a link to the Custom categories & multi category transactions Feature Idea. I like it!
It feels like an important point from @hugo – the challenge to keep things as simple as possible without users having to think. Reminds me of Steve Krug’s Don’t Make Me Think.
Perhaps offering the ability to capture spend on cash withdrawals and not supporting multiple/custom category transactions could be a way for Monzo to experiment with this idea using a focused use-case. Some of the learnings from this experiment might help future experiments with multiple/custom categories.