Some MacOS users are having some issues. The launcher itself was not updating itself to 1.16.3 and I had the same problem. I reinstalled my Minecraft hoping that it will fix the update issue however i came across this problem which does not let me play minecraft and leave me at the launcher with the system's notification to check my configuration, no versions or snapshots are available or seen in the version list below. uninstalling and reinstalling minecraft did not fix this issue.