I keep a personal library (of physical books) for this reason. People often underestimate the value of spacializing knowledge. I write in the margins, mark them up, and leave scraps of paper with notes. Then I put them on shelves in broad categories - for me that’s things like architecture, design, technical, photography, philosophy. The result is a system thats’s easy to retrieve from, and importantly, easy to browse. The spines become symbols for collections of thought. I have yet to come across a piece of software that more effectively facilitates drawing inferences and connections from deep material. IMHO everything else can be found on Google.