Help me finding this alternative guitar tuning

[u/Calm-Scar4886]

https://youtu.be/iCpX5p12j6M

Hi everybody,
I'm racking my brains trying to figure out what tuning was used in this song.
I noticed that during a live performance the guitar player used a CGDGBD aka open G/C tuning,playing a basic major chord, but the very first chord of the progression sounds slightly different from the studio version.

It should be some kind of math rock/emo tuning .