I am using Unity 2020.0.0f1, Playmaker 1.9.0 this is on a new build I started today for the WebGL platform there are 125 errors and 411 warnings. The Playmaker tab doesn't show in the toolbar, so I can't put in an error report. This lack of Playmaker tab is consistent in my current builds as well.
Most of the errors are various CS0246 looking for elements that are missing such as "Library\PackageCache\com.unity.package-manager-ui@2.0.3\Editor\Sources\UI\PackageDetails.cs(607,17): error CS0246: The type or namespace name 'Button' could not be found (are you missing a using directive or an assembly reference?)" but several hundred lines of this. I've got the developer error code list it's just too big to attach here. If you want to send me an email adress I'll forward it to you.