Will Power BI still query data if the data is not used in a visual? The model and data source are still technically there but if it's not actively used does the data still get pulled?
If you are using IMPORT MODE: Yes, the data is completely pulled into the data model and RAM, no matter if it is used to calculate a visual or not.
If you are using DIRECT MODE: No, only the data needed for the visualizations (this includes slicers) is pulled into memory.
Read the docs: https://learn.microsoft.com/en-us/power-bi/connect-data/desktop-use-directquery