Hello aaaa1468,
Thanks for asking the Apple Support Communities about lines on your computer display. I am happy to help.
First, verify if the issue is also occurring in macOS Recovery: About macOS Recovery - Apple Support
If there are no lines in macOS Recovery, test if the issue is occurring in safe mode. Safe mode will tell us if the issue is related to a startup item or plugins, and sometimes is all that is necessary to correct some problems. When you boot to safe mode, log in to your account and check if the issue is also occurring in safe mode or not. Use this article for the steps to get into safe mode: Use safe mode to isolate issues with your Mac - Apple Support
If everything is working properly in safe mode, but then is not working after you restart the Mac, please check the section titled "If an issue doesn't happen in safe mode" for the next troubleshooting steps.
If the issue is also occurring in safe mode, move on and test if this problem occurs in a newly created unmodified test administrator user account on your Mac. A test user will let us know if the issue is isolated to your account, or system wide. Please check this help article: How to test an issue in another user account on your Mac - Apple Support
After you are done testing, please check the section related to results, titled "If the issue happens in the other account" or "If the issue doesn't happen in the other account”.
If the lines are also present in macOS Recovery, I recommend having the computer checked at an Apple Authorized Service Provider or Apple Store. Please make a backup before taking the computer in: Use Time Machine to back up or restore your Mac - Apple Support
Also, you will need to have your Apple ID and password handy when visiting a service provider. Also, please check this help article under the bottom section titled "Get ready for service" for other items to ensure you are prepared: Mac Service and Repair - Apple Support
You can find a service provider using this link: Apple Find Locations
Thanks again and have a great rest of your day.