Iphone displaying green lines can't restart it

A Forced Restart will almost always perform, unless there is a physical issue with the buttons. But you are on the right track, and it can take a few tries to get a Forced Restart right. Be sure to perform it quickly and ignore the Power Off Slider that appears midway.

• Press and quickly release the Volume Up Button
• Press and quickly release the Volume Down Button
• Press and hold the Side Button until you see the Apple Logo

Then if that doesn’t help, I would suggest service at your nearest Apple Store Genius Bar or an Apple Authorized Service Provider, as there could be an issue with the display.

Apple Store Genius Bar: Genius Bar Reservation and Apple Support Options - Apple

Apple Authorized Service Provider: Find Locations

I recommend service.

Service Checklist:

• iPhone service pricing.
• Check AppleCare Coverage.
• Get your iPhone ready for service.

Click ▶︎ Start a Repair Request.

Need more help?

• Call 1-800-APLCARE.
• Contact Support.
• iPhone Support.
• iPhone User Guide.

Click ▶︎ Check Repair Status. 🔧

Good luck! 👋🏼😉