An external display is a negotiation between the computer's video output, the cable and the panel. Each has a maximum resolution and refresh rate, and the connection settles on whatever all three support.
That is why a high-resolution monitor can run at a lower resolution without warning: an older cable or adapter cannot carry the bandwidth, so the system quietly picks a safe mode.
Blurriness often comes from scaling instead. Running a panel at anything other than its native resolution forces interpolation, and text is the first thing to suffer.
Refresh rate is a separate setting that frequently defaults low. A panel capable of high refresh may sit at the minimum until it is changed manually.