Click on Puzzle Dashboard and hover your mouse over the lowest rating in the center of that web. It's not the number of puzzles you do, it's that lowest value that you only can see that needs to be improved.
lichess.org/training/dashboard/90/dashboardlichess.org/training/themesChange the number of days and that lowest value changes too with a different tactic. You then find the tactic in themes to correct your weaknesses. Press ctrl F and type the tactic name to located it quickly.
Probably the weakest tactical rating we have are the themes we have not done. And we wonder why we are not improving. We are practicing only what we know.