Chris Webb explains how data type conversions and query folding might not mix:
It’s surprisingly easy to stop query folding happening in Power Query by changing the data type of a column. This is mentioned in the docs here, and it’s something several people have blogged about already (for example here). However there is something new to note: an option that will allow you to convert text columns to number or date columns in a foldable way for SQL Server data sources.
Consider the following table in a SQL Server database that consists of a single nvarchar(50) column containing numeric values:
Click through for the example, and also check out the comments below for more info.