QLED is more a range name then a display type.
If it refers to a specific technology that's backlight units which use a combination of blue LEDs and a quantum dot enhancement filter (QDEF) to achieve their output instead of more traditional methods like coating the LEDs in different phosphors.
They can produce a wider colour gamut (e.g. for HDR content) but the colours filters on the opposite side of the screen are currently a big limiting factor there.
It's obviously only applicable to display types that use a backlight, which is primarily LCD.
It has nothing to do with other aspects of the display like the pixels.
QDEF is a decent technology and technically produces the best colour gamuts without the variable ageing issues RGB LEDs suffer from but they've never really been a huge leap over the alternatives.
Various other uses for quantum dots are in development that are likely to have a bigger impact, such as quantum dot colour filters/converters.