It's not for me to judge what you do with your new rig outside of gaming—I just hope you're taking the necessary precautions, and set up your anti-virus of choice at the first opportunity. Microsoft Defender is better than nothing, except for when it says it's been turned off when it actually hasn't.
Apparently, this is a known issue in Windows 11 and Windows 10. Microsoft details the issue, writing, "Notifications might appear stating that 'Microsoft Defender Antivirus is turned off,' even though the antivirus is functioning correctly and all settings show it as active. These notifications can appear when Windows starts and intermittently afterward."
Worse still, these fibbing notifs can "persist even if notification settings are turned off." But worse than that, the issue can be observed in "any version of Windows or Windows Server with Microsoft Defender Antivirus running with the latest Defender updates."
English (US)