Hi.
Windows Defender can of course scan USB offline. Specific steps are as follows:
Settings>Update and Security>Windows Security Center>Virus and Threat Protection>Scan Options>Custom Scan, select the USB you want to scan, and scan offline.
For details, please refer to this document:
https://learn.microsoft.com/en-us/microsoft-365/security/defender-endpoint/microsoft-defender-offline?view=o365-worldwide
Hope the information is helpful.
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