I'd expect the number to be in the low double digits. 10-20% on the total by now. But in the high double digits for pre-orders / early-access and starting the hype train. Say 70%. I haven't met a tabletop RPG player that hasn't played BG3. Though in the more hardcore circles I know there are those that don't play video games at all...

But I can also safely say that DoS players don't account for the success of BG3 since those games never had mainstream appeal. Brand recognition is for sure a massive factor. Also keep in mind that Baldurs Gate, particularly 2, is considered a must play to understand the evolution of western RPGs. While the PC gaming market was much smaller back then so many people will have played it, read about it or wanted to play it but couldn't get past the aged mechanics and looks since then. Its sales numbers belie its influence and reach.

Finally I'd say a good 50% or more of the total buyers bought in after it was apparent that it was going to be GOTY, so many were talking about it and every critic was singing its praise's, but it wouldn't have gotten there without that brand appeal and the super rich and deep lore which the "power users" (like many critics and early adopters) crave.