System scaling and viewport

Hey. I noticed when I’m using system scaling on mac os, the browser’s viewport changes. I have a 4k monitor and this only happens if I scale it to 1920 1080 “size”. The viewport of the browser is not 1920 1080 anymore but something like 1440 because I can see CSS styles that I only want to show on laptops’ resolutions (1440 breakpoint). So it is not only just bigger text, but different css as well. This is only happening with safari. Now, I’m not going to waste too much time on this, because If someone’s viewport (because scaling) is 1440 width on a 1920 screen I can’t help him too much, but just want to be sure, so I just want to know if someone maybe knows how to overcome this?