From what I read here (https://www.gm-parent-visas.com/number-of-parent-visas-capped-for-year-to-30-june-2021/) the cap was not reduced to 3600 from 4500. 4500 was announced as the total parent visa number, it was just divided into two parts: 900 for non-contributory visas (103/804) and 3600 for contributory visas (143/173/864/870). I guess it will be the same for 2021-22.