Thanks, FelixIvy.  Just to clarify, the reason you can't use temporary views to load a materialized view is because materialized views (like regular views) must be created using a single query that is saved as part of the view definition.  So the solution in this case is to rewrite the temporary views as ctes or subqueries, so all of the code is in one single query -- as if it were a regular view.

Or, if the code is complex enough, it may be cleaner, more visible, and easier to maintain and optimise to leave the code as-is, in a notebook:  load the data into a table, and then schedule the notebook to refresh the data in the table periodically.