Is there a way to use WAC to install only Critical Updates on servers? I normally don't install the Recommended Updates, just the Critical ones. I am using 1904.1
Unfortunately you cannot filter which updates to be installed with Windows Admin Center (WAC) alone, you can however centrally manage updates on all of your servers by using Azure Update Management.
In Azure Update Management you can for example select all the update classifications that you need, or include/exclude updates.