is it true approx 12 million people in Texas are currently without electricity?

Yes, many, not sure if it's approx 12 million

Because of a snowstorm

It's about 4 million people:

https://www.newsweek.com/ercot-power-outage-map-up...

I am guessing you are a foreign troll and that is why you don't know all of the southern USA is experiencing a severe winter storm which is causing all kinds of havoc and not just power outages.  

There's another reason. When precipitation falls and freezes on tree branches, eventually, the weight can cause the branches to break and fall on power lines. We have an occasional ice storm where I live, so the power company has done an extensive job of cutting back any tree branches that hang over power lines. That seems to have helped in the current situation. They don't get much snow and ice in Texas, so they probably weren't prepared for it.

Then you have the idiots who try to get out and drive in the ice and snow, with no experience with it, and slide off the streets into the transformers, putting the power out for a whole neighborhood. 

Massive Arctic blast with sub-zero temperatures and heavy snow causes a spike in both electricity and natural gas use.  

The temperatures cause the gas wells to freeze and the wind turbines to stop working and solar farms are covered in snow.

These cause a critical shortage of both electricity and gas, so in order to conserve both, rolling blackouts are implemented.

This is a very good reason why green energy needs to be rethought and can't be implemented in the way it's headed as this would not have happened with coal powered plants.