I have an absolutely huge project folder split into hundreds of topics, and a master ToDo in Excel used as a kind of Kanban/white board, with development notes in Word.

It's clumsy AF - the Excel part works, the Word part could be better - but it's a working solution of sorts, with everything synced across all my devices so I can make some notes on my Macbook while out and then pick up the thread at my desk later.

I tried all the usual alternatives - Trello, Org Mode, paper notebooks, real white boards, and so on - and so far this is the most productive.

take that UML