Hi Pranshu,
It sounds like you've done what you can to ensure that this isn't a software problem, so yes the next logical step would be to replace the screen. Although there are also chips on the motherboard that handle the touch screen, by far the most common point of failure for touch issues is the screen itself.
Of course, with modern phones the OLED is fused to the digitizer, so they can't be replaced separately and need to be bought as a single assembly. iFixit has a guide showing you step by step how to do that replacement, and you can even support their repair efforts by buying the screen directly from them if you like. Otherwise they should be readily available on sites like Amazon, eBay and AliExpress, among others.
[guide|132740|OnePlus 5T AMOLED Screen & Digitizer Replacement - iFixit Repair Guide|new_window=true]