How can I deactivate the transmission for individual showreels at Spotlight ?

When creating a new showreel, you have the option of configuring the visibility of the showreel and can deactivate the transmission to Spotlight by deselecting the "Visible at Spotlight" option:

For existing showreels, you can adjust the setting at any time by clicking on the "Visible at Spotlight" option for the respective showreel. You can change the visibility in the form that opens.