In this case, you need to download the Platform Tools to run the ADB command, which is necessary to sideload apps on Windows 11 using Windows Subsystem for Android.

Using the command prompt on your computer, navigate to the "Platform-tools" folder of the SDK. Type in "adb devices" (without the quotes) and hit the enter key.

Once you’ve downloaded the Platform Tools package, extract the contents of the .zip file to a folder you can find later (like “C:\Android\platform-tools”).

You can get the platform tools for Windows, Linux, or Mac direct from Google's servers. You get a ZIP file containing the platform tools folder with ADB, fastboot, and a few other tools.