If you (like me) couldnt find the "Block notification page" option in a recent ZenArmor version on OpnSense; thats because its not included in the "Free" license. Its included in the 99/year Home licence however.
Source see "Customized Landing Pages for Blocked Sessions" at https://www.sunnyvalley.io/plans
Source see "Customized Landing Pages for Blocked Sessions" at https://www.sunnyvalley.io/plans