You may need to map a back paddle or specific button to "Tab" and add a sub-command for "Alt" in the Steam Input settings to simulate the press.
By following this guide, you should be able to use the Alt Tab feature with Moonlight and seamlessly switch between windows while streaming games from your NVIDIA GPU. moonlight alt tab
If you are using a physical keyboard and Alt+Tab is still intercepted by Android (common in newer versions like Android 15/16), try using the Windows + Tab combination instead. Troubleshooting You may need to map a back paddle