Check your Windows Settings > Update and Security, and click on Open Windows Security. Then click on Virus and Threat Protection on the left side and then click Microsoft Defender Security Options. From your description it sounds like you have Periodic Scanning turned on. That allows Defender to run periodic scans alongside your Norton product, but it does not enable any real time scanning that would conflict with Norton.
If you no longer want to see those scans, just turn that feature off.