I’m interested in this too – to be able to change colours by query or rule. An option is to port the data to Power BI and set it up there.

While you can only have pseudo thematics based on list values, there is a work around using queries and individual styles. A common example of this is where we have a text calculated field tracking a range of activities at a site and the calculation returns a value of Proposed, Started, Partially Completed and Completed. In this case a style is setup for each value and we have a query to subset based on the value. Each query subset is added to the Project and the corresponding style added to the query. Additionally, we apply a Form Variant with a behaviour of Map Display Only to the query subsets and this prevents multiple selections being presented when opening from the click point.