Hi @Dom
I found a similar thread for you that mentioned that the solution is to add a parameter that doesn't allow null values to prevent the report from running at the beginning. For more details you can refer to the discussion in this thread: https://stackoverflow.com/questions/277714/sql-server-reporting-services-how-to-stop-a-report-firing-when-opened.
I did a simple test. Added a parameter "stop". When previewing, the report will not render.
If the answer is helpful, please click Accept Answer
and Up-Vote
for the same. If you have any questions, please feel free to let me know.
Best regards,
Aniya