Hi, and thanks for reaching out. My name is Bernard a Windows fan like you. I'll be happy to help you out today.
I understand the issue you have, there is nothing to worry I am here to help, for us to disable the real-time scanning and protection of McAfee you just need to open the McAfee app click PC Security, and turn off all on that page.
In addition, to switch to Microsoft Defender, you need to completely uninstall McAfee you need to download the McAfee removal tool:
Go to this link: https://www.mcafee.com/support/?articleId=TS101...
Under "How to remove McAfee software from your Windows PC"
Follow "Option 2 — Remove using the McAfee Consumer Product Removal tool (MCPR)"
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
Let me know how it goes and I hope that helps.
Bernard