[rob]

2560x1440 and ~12px on HN looks incredibly small.

I just switched the resolution to 1024x768, and now the same ~12px is "larger" and easier to read without needing to increase my browser zoom.

There's an obvious visual difference between the two.

[SassyBird]

Without HiDPI (sic!) scaling that means that a correctly-sized display for that resolution would have a 30" diagonal on Windows (standard PPI: 96) and 40" on Mac (standard PPI: 72). If you don’t have HiDPI (sic!) scaling enabled in your system and your display is smaller than that, then you’re basically browsing everything zoomed out.

[account42]

Then your setup is not compliant with web standards. Most likely you need to enable DPI scaling somewhere.