Nothing is stopping the other 18 countries from forming the G18.
Or inviting 2 more members other than Russia and China and naming it the New G20.
Well India is still doing brisk business with Russia and importing plenty of Russian oil. Same with with Pakistan, Indonesia and most Asian countries who refuse to impose sanctions on Russia.
We are talking over 50% of the world’s population here.
What’s the use of the G20 anyway?