“The UN has mighty achievements behind it, but some of the slowness of bureaucra

“The UN has mighty achievements behind it, but some of the slowness of bureaucracy and cumbersome procedures that were necessary to keep everyone on board in the Cold War years should be reformed.” (Clare short)
How is the UN reforming itself to deal with the post-Cold War international system? Which institution, the G20 or the UN, is well suited to address pertinent challenges of globalization and the Covid-19 pandemic, as well as the economic gap between developed and developing countries?