The current NuGet.org repository signing certificate will be updated as soon as March 15th, 2021. If you validate that packages are repository signed by NuGet.org, you will need to take steps to avoid disruptions when installing packages from NuGet.org.
The current Microsoft author signing certificate will be updated as soon as November 1st, 2020. If you validate that packages are author signed by Microsoft, you will need to take steps to avoid disruptions when installing Microsoft packages.