One of the possible reasons was too much sun power and not enough demand. Solar and wind are unreliable.

No.

The issue wasn’t that there was too much generation, or that it is unreliable.

It was a grid issue, it wouldn’t have mattered what generation was used (solar, wind, gas, nuclear, coal, etc…).

Don’t be mislead by everyone who jumped on the coal bandwagon a day after the incident before we even knew what the cause was.