Hi Joyce
It depends on where the vehicle is driven...e.g. freeway or city driving as the hybrid system needs to regenerate to optimize the economy so this is a major consideration
Here is a useful comparison between the two model versions
https://www.lexusofseattle.com/compare-2020-lexus-rx-350-vs-2020-lexus-rx-450h-lynnwood-wa/#:~:text=One of the most significant,and it offers 295 horsepower.&text=In comparison%2C the 2020 Lexus,powertrain with a hybrid component.