Call me old fashioned, but I still just use note cards. Obviously portability is an issue, but I don't travel much (1 long trip a year pre-covid), so never ends up being a real problem.
This would be practically impossible with a physical system. In addition to the fact that your memory of a new cards fades faster than cards you saw a long time ago; taking the time to approximate such a system would be a large burden that software can just handle for you.
But I did my own version of spaced repetition -- when a card was really hard, I'd put it back in the deck just 5 cards back. If it was easy, I'd put it all the way in the back of my ~200 cards, or eventually remove it entirely. Or wherever it was in between, I'd slot it at an appropriate distance. It actually worked really well.