This sounds strange. I did a simple test. All three parameters in the report have default values. When opened in a browser, the parameters area expands when there is no command or when "&rc:Parameters=True" is entered. When I type "&rc:Parameters=False", the parameters area is hidden. Everything works great.
What browser are you using? When you pass configuration on a URL and it crashes, check the logs for error messages: https://learn.microsoft.com/en-us/sql/reporting-services/report-server/report-server-service-trace-log?view=sql-server-ver16.
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Aniya