Sebastiaan de Man: Create Customized Knowledge Articles with Flow
Starting with a Salesforce Knowledge article, insert variables using the {!VariableName} convention like this:

Create a flow that has these variables as … variables

Use the recordId variable to get the KnowledgeArticle record, based on MasterVersionId:

Get the fields to show:

Set the variables with the values you need to use (I used default values for this flow)
Make a screen component that show the fields:

Add the flow component to the Article detail page in the community, pass over the recordId:

And it will magically replace all variables in the text:

Additional Resources
Salesforce Knowledge and Flow Wiki Page
The Flow Troubleshooter Pattern is useful for creating and managing large numbers of custom nodes without having to manually add a flow element for each one.