What’s the reference screen resolutions to start preparing mockups for desktop?

I need to justify my choice of screen resolutions for a PWA desktop app that runs to run on old and newest PCs. So far mockups are preapred for 1440? I don't have specific information which lead to simple decision of downscaling or upscaling. Maybe there is some market standard which i don't know about or some good practices in this topic. Thanks in advance. This is my first topic ever.