For a Surface Duo 2 with the Power/Fingerprint button physically missing, the safest approach is to use a software restart rather than a complete power-off until you have finished transferring your data.
Recommended options
- Accessibility Menu — no computer required
Go to:
Settings → Accessibility → Accessibility Menu → turn it ON
Enable the available shortcut, such as the floating Accessibility button.
Open the Accessibility Menu and look for Power. If your Duo 2 presents the Android power menu, choose Restart.
- ADB from a Windows PC — most reliable
If USB debugging is already enabled:
Connect the Duo 2 to your PC.
Open Command Prompt where Android Platform Tools are installed.
Run: adb devices
then:
adb reboot
or,
adb shell reboot -p
to completely power it off, but I would not recommend doing this yet. With the physical Power button gone, turning the Duo 2 back on could become difficult.
Since you don't intend to repair the Duo 2 and only want to keep it operational long enough to migrate everything:
Keep it powered on → transfer your data → use adb reboot whenever it starts misbehaving.
I would avoid a full power-off until the migration is completely finished.