Take a look at the current latest version page: https://mvnrepository.com/artifact/net.sourceforge.plantuml/plantuml/1.2021.0
You will notice the following message:
According to this page the versioning scheme changed in 2017, so this version is very out of date.
It is even more confusing because of the amazing backwards compatibility. All of the features I was using worked perfectly fine, except they had tiny quirks e.g. stereotype could not be separated with a space from the component name.