Game gets slower for certain resolutions in Unity Editor. What could be possible fix?

Hello,

I am developing game for mobile and I have have make sure that it runs smoothly for all resolutions. So to do this I am testing my game in different resolutions(portrait mode) in Unity Editor.

In my case my game works fine for these resolutions : 1280 x 720 , or 16 : 9 to 18: 9 (aspect ratio)

But it gets slower for these resolutions : 1920 x 1080 , 2160 x 1080, 2560 x 1440 , 2960 x 1440

I am doing my physics in Fixed Update, I am using time.deltaTime for movements, minimized the use of UI's, reduced some code.

I did profiling and it shows rendering usage as higher. I tried optimize things for that but didn't work.

Thanks and Happy Christmas!