You would have to pry https://workflowy.com from my cold, dead hands. It's the best outliner I've ever used and they actively resist adding features that would only please a subset of users. It offers excellent cross-device synchronization and works nearly as well on a phone as it does in a browser or desktop app context. You can attach notes and share at the node level, either via read-only link or collaboration invite which allows others to graft your shared hierarchy to theirs. It has well-considered keyboard shortcuts.

Most importantly, the search is intelligent and works instantly... even across my 100,000+ nodes.

My entire life is in Workflowy. I am thrilled to pay for my annual subscription, because the value I receive is outrageous.