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VisualStudio doesn't provide the offline dubugger mode. To debug the mode, we need to keep the connection and start the app with the debugger attached to the app process(Debug > Start Debugging).
Check the doc:
https://learn.microsoft.com/en-us/visualstudio/debugger/debugger-feature-tour?view=vs-2019
If you don't want to connect an Android device to a computer using the usb cable, you could use wifi connection instead.
https://learn.microsoft.com/en-us/xamarin/android/get-started/installation/set-up-device-for-development#alternate-connection-via-wifi
Best Regards,
Jarvan Zhang
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