Large increases in dollar reserves tend to come during periods of dollar weakness, not periods of dollar strength. That is for a simple reason: many export-heavy countries still intervene heavily in the foreign currency market to try to keep their own currencies from appreciating against the dollar. Until Asia is as willing to float up as it is to float down, the dollar isn't going anywhere as a reserve currency.
Right now the bulk of the IMF's lending capacity likely won't be used in the face of the economic, financial, and public health shock from COVID-19. Mobilizing the IMF's lending capacity likely will require a new facility. The Short-term Liquidity Line created this spring isn't actually well suited for the moment.