So that's the issue. The problem with oneplus and Oppo charging technology. They are in no way the same as USB PD charging protocol. So no way you gonna charge the pixel 7 at a faster rate.
One thing many people still not very sure or aware of with the charging technology of the phones they buy.
Now in market, the Chinese phones are the one that went off rail and balls to the walls kind of fast charging technology without following USB specifications. None of their supplied cables also follow USB specifications.
So using their cables or the adapters to charge any none Chinese phones can meet up with issues such as slower charging or intermittent charging rate etc.
There are reasons why Samsung also have moved on to USB PD charging. So does the Pixel phones. Cause nowadays even some newer laptops adopted the USB PD charging.