If your battery health is okay, it might be a hardware (screen? other internal component?) failure or false contact, but we, just users like you, cannot diagnose that kind of issue remotely, sorry.
I suggest that you contact Apple Support directlòy, using this link:--> Contact Apple for support and service or make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region . After checking it out, they'll give you all the available options.
Regards
Giulio
(*) You can do it: