I used to do that with sheets of A4 paper. Eventually, I had a "master sheet" with a list of projects and ideas that I was working on or thinking about. With separate sheet(s) for details.

But I found it frustrating when I was away from those sheets and wanted to update them. So I switched to a mindmapping app called MindMup. Which I learnt to rely on. Especially as it allows collaboration with colleagues.

Since retiring, I stopped my MindMup subscription. And I really missed it at first. But I soon found Gitmind which gives me back all that I lost. Plus a whole lot more.

!BBH