Hi there,
I'm Cherrelyn and I'm here to help.
If you really need to turn off Microsoft Defender completely, you can do it through Windows Security settings or the Group Policy Editor (on Pro editions). Just note that Windows will often turn it back on automatically for protection unless another antivirus is installed. If your reason is to run specific software, consider adding it as an exclusion instead his keeps your system protected while avoiding false flags.
I hope this will help and If you have any question please feel free to ask.
Warm regards,
Cherrelyn