Should I use Windows or Mac for WordPress theme development

Hello good people,

I have been started PSD, HTML and WordPress theme development from 2019. Recently, I am getting some soft rejections for color contrast, spacing and HiDPI displays graphics blur issues.

Currently I have windows desktop with 21" 1920x1080 display.

I am confused about what should I do for HiDPI displays? Should I switch from windows to Mac or just change display in windows desktop?

If Mac is better, which device will more suitable - Macbook pro or iMac or Mac Mini ?

That has absolutely nothing to do with it. HiDPI issues means that you are most likely using low quality graphics in your themes, whatever it is photos, or illustrations or whatever, impossible to say without seeing it. Thinking that buying a Mac will make you a better designer is extremely naive. I mean if you can afford it then buy it, I love my Macbook, but you certainly do not need it to make a WP theme. You do not need a HiDPI display to make HiDPI designs, you just need to understand how it works.