480p is considered "Standard Definition" (SD). While it looks acceptable on small mobile screens, it may appear blurry or pixelated on large 4K monitors because the software must "stretch" the limited pixels to fill the screen.
In some cases, a Windows Update can reset display settings or cause driver conflicts that lock the monitor resolution to 480p or 640x480. [@MY_Update] 480p
Are you experiencing this resolution limit on a or streaming platform ? 480p is considered "Standard Definition" (SD)