Maybe this can help too (org-roam-review) :
(However, I have not yet tested it. )
This can also be interesting
org-drill.el – flashcards and spaced repetition for org-mode.
Finally, I was also considering creating my own system (of flashcards in particular. I don’t know if flashcards are “good enough”, maybe I should implement a larger space repetition system that could make flashcards work).
If you’re ever interested, I can give details of the theory, but I haven’t had time to do anything yet (I prefer to look at the above solutions in detail first)
I will keep up to date with this topic, as implementing a space repetition system in org roam is almost a must: making your second brain is useless if you forget it 
Don’t hesitate to give your opinion on the various solutions proposed
Ps: Maybe you’ve already seen it, but this post may help too