As @ptillisch mentioned in another thread, the UNO Q board simply does not have the capability to cut off power completely while showing the onboard green power LED as off.
To avoid the quoted re-boot situation, I follow these steps:
1. Stop app in App Lab or Quit IDE.
2. Open ADB shell from Cmd Prompt or from >_ icon of App Lab.
Response: arduino@ArduinoQ:~$_
3. Issue the following command:
sudo shutdown -H
Response: [sudo] password for arduino:
Action: enter Linux password (characters are not seen)
Response: Shutdown scheduled for Tue 2026-05-12 09:42:38 UTC, use 'shutdown -c' to cancel.
arduino@ArduinoQ:~$
4. Wait for 20-sec and then unplug the USB power/data cable. (Otherwise, after ~60-sec the sell window exits to Cmd Prompt and UNO Q reboots.)
5. Shell window exists to Cmd Prompt.
Response: C:\Users\GolamMostafa>
Note: In my Windows based PC, i do the shutdown session. All the opened files are closed and then power is automatically cut off. I am interested to know what happens to the PCs running Linux OS.