Hi,
Unless there is something going wrong with the main board display IC, you can try doing a backup & then initiating a DFU recovery.
DFU is a deeper recovery process if no other method works.
Caution ⚠️ DFU should not be used on an iPhone that has had damage to main board or been water damaged as it can cause unrecoverable problems or totally brick the phone.
You can search for DFU restore on YouTube to see how to execute it.
You can do this through iTunes on PC or in the new Apple recovery app for PC.
You can also download and use 3u tools on PC or Mac, either option will prompt you when detecting a device in DFU mode, then you can try the recovery.
If the device is detected in restore mode (connect to iTunes), you will have to disconnect and try again until the prompt on the app says device is in DFU mode.
If using 3u tools, once in DFU mode you can flash the phone for recovery with the firmware that you downloaded.
Apple app will do this automatically.
Hope this helps