What's the main instrument or sound used by the synthetizer in this youtube video?

Awwww It’s gone for me.

Your Youtube is not available in the USA ?

I just checked and it says “this video is no longer available”.

It’s online again.

“This video isn’t available anymore”

Is it an Italian video ?

Try this: https://www.youtube.com/watch?v=D-_DtNLzbX8

Strings probably violins.

I might just be crazy, but it reminds me of binaural beats

I don’t think it is an instrument. They play two tones/frequencies that give an illusion of a third. This sounds like one edited to be more musical and angelic sounding. Hard for me to explain, just my first thought when I heard that was binaural beats.

It’s just generic synth sound. Any mid to pro keyboard has it.