A physical Leitner box is the most effective way to go from intermediate to advanced. Wiki it.
However, as the number of card starts to increase and one’s work ethic as they can ever debris it’s below what is needed to do section 1’s reviews each day, there are alternatives to giving up together.
namely what is needed is to create a reserve of unreviewed cards which are not yet added into the rotation. Call it “New” and don’t keep it in the leitner box all. Every once in a while when you’re having a good day, make a couple cards from this new section & add them into the rotation (i.e. section one)
And when a Card retire from section 7 (or 8), give it a retirement party.