Mindmap tools generally don't work for this because they want a single topic for each map, and all the words on the one page. KM/KB tools don't work because I can't just draw the relationships between the points, I have to go in and actually create notes that I then get to visualise.
I really wanted to like Obsidian, but the way it treats folders puts me right off. I tried Neo4j Bloom, but there are UI difficulties and it's not really great for notes. I'd build it myself but I have no idea where I'd even start on a UI.