"Myriad" itself implies a large, uncountable number. It's similar to words like "many" or "countless" and doesn't need a preposition like "of" to specify the quantity.
Here are some examples:
* Correct: A myriad of stars twinkled in the night sky.
* Incorrect: A myriad of the stars twinkled in the night sky.
* Correct: The artist used a myriad colors in her painting.
* Incorrect: The artist used a myriad of colors in her painting.
However, there are some specific cases where "of" can be used after "myriad":
* When listing specific items: "He faced a myriad of challenges, of which the biggest was funding."
* When referring to a specific group: "The concert featured a myriad of artists, of whom many were local."
In general, though, it's best to avoid using "of" after "myriad" unless absolutely necessary.