Hi
At the moment I think it’s safe to assume that it’s not malware, malware usually does much worse thing and malware is very rare on iPhones
Also burn in is quite uncommon on iPhones that have Original displays,more common on 3rd party displays but still quite uncommon
what I think the issue is most likely to be is a dislodged display connector
It could also be debris but I have seen this happen on iPhones and iPods when the ether the display is damaged, connector isn’t seated properly or the connection has debris and needs cleaned with isopropyl alcohol
Might be worth trying the above before replacing the anything ,it’s entirely up to you:-)
Hopefully this helps
Any questions please ask
Thanks:-)