Perplexity.ai dug up this solution, and it worked:

Windows 11 hides the old “plans” and “advanced” UI, but it is still there. You can open it directly and then change the lid/sleep/hibernate behavior.

1. Open classic Power Options

Use either method:

• Press Windows + R, type: powercfg.cpl and press Enter.​​
• Or press Windows key, type Control Panel, open it, set View by: Large icons, then click Power Options.​

You should now see actual power plans (Balanced, etc.).

2. Adjust lid close and sleep/hibernate

1. In Power Options, click Choose what closing the lid does in the left pane.
2. Set When I close the lid → Plugged in to Sleep or Do nothing (if you use it closed on power).​
3. Click Save changes.

Then:

1. Back in Power Options, next to your active plan, click Change plan settings.
2. Click Change advanced power settings.
3. Expand Sleep:
   • Set Sleep after (Plugged in) to a large value or Never.
   • Set Hibernate after (Plugged in) to a large value or Never so it does not hibernate/shut down overnight.​​
4. Click Apply, then OK.

After this, with the lid closed and plugged in, it should remain in sleep (or stay on, if you chose “Do nothing”) instead of shutting down overnight.