Just to be sure, the steps described there are done in Mendix Studio. If you do it in Mx Studio, you can literlly follow the steps.
If you do want to do this in Mendix Studio Pro then you could filter the data using a database source constraint: https://docs.mendix.com/refguide/database-source#constraints or using an xpath constraint https://docs.mendix.com/refguide/xpath-source on the listview.
For Mx Studio if you follow the steps accordingly, it would be done. You just have to select the three horizontal dots in filter menu and type “Followup_needed” in where section and “true” in is section. Also check that you have taken “Followup_needed” as “Boolean”.
If you are using desktop modeler i.e. Mx Studio Pro then while selecting data source for list view, add a constraint selecting “Followup_needed” with value as “true” in “Constraints” section.