Retention and understanding Problems.

Hello everyone, i've been doing THM for a while now and i'm having big trouble. Every time i finish some rooms like for example the OWASP TOP 10, or The juiceshop i tend to forget most of it very easily because my deep learning skill isn't very good (i.e. understanding the concept in depth), and going back to the same rooms every week sounds pretty dreadful. I tried taking notes in obsidian but that takes a while and it's the same as going back to rooms. Tried making flashcards but the negative is that it takes me 2 or 3 times more time to get the rooms done than needed. Tried recording audio and relistening to it which seems to help a bit but it still takes me longer to complete the rooms. Any advice in general for learning concepts ? Thank you !