@Michael van Olden Welcome to Microsoft Q&A forums and thank you for your interest in Azure services.
The WordPress solution you installed from Marketplace combines all the required resources into a package that is easy to deploy.
This way you don't have to provision the resources independently and configure them.
Once deployed, you have complete control over the resources and can manage them independently.
You can scale the app and database separately.
Coming to your question on Autoscaling, you can configure the triggers that can scale up or scale down the database.
For instance, when CPU utilization exceeds 70% or when utilization falls below 30%.
Please check the below article for step-by-step instructions
Auto Scale Azure Database for MySQL Using Azure Automation
Do let us know if you have further questions.
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