A MiniLED display is a traditional LCD display, but the backlight is divided into addressable sections called dimming zones. A few of Apple's high-end displays use this technology. The downside is that each pixel isn't 1:1 with a dimming zone, so there are "blooming" artefacts where a zone overlaps a region that needs to be lit up.

MicroLED, much like OLED, is where each pixel self-illuminating. For OLED there are organic materials that emit light in the red, green, and blue. For MicroLED each individual sub-pixel is an LED.

Making a MiniLED display isn't too hard, depending on the number of zones. Making a MicroLED display is quite hard because the LEDs need to be microscopic and also there need to be millions of them. There are some MicroLED displays available for sale today, but they're huge (you don't need the LEDs to be as big if the display is massive), and they also cost hundreds of thousands of dollars, e.g. https://www.samsung.com/us/televisions-home-theater/tvs/micr....