I have a largish white board (thanks home office) on which I summarize a (sub)section of a book / online course in my own handwriting / symbols / diagrams after

I have a largish white board (thanks home office) on which I summarize a (sub)section of a book / online course in my own handwriting / symbols / diagrams after reading / watching it first and doing the summarizing on a second run (after which I take a photo and save it to a doc on the topic). This method has helped me commit quite a lot of conceptual information into long term memory - but - it is time consuming. If I ever need to refresh my memory on a topic, I pull up the photo and redraw it - sometimes adding or changing things a bit - then take photo again. Rinse and repeat.