I based my answer off the high school students I am around. I cannot think of one student that plays that does not watch Stranger Things. It would be like asking us as kids how important the Lord of the Rings books were to our interest in D&D. Or, at the least, the Conan movie. In the end, it is not the most important thing, but it is pretty darn important to the younger generation of players.
On a personal note, despite literally everyone telling me to binge, I have not found the time yet to watch the show.
That might be putting the cart before the horse IMO.
I read fantasy novels and play fantasy video games because fantasy appeals to me, which is also a big part of why D&D appeals to me. Had I been introduced to RPGs prior to novels and video games, I inevitably would have still read fantasy novels and played fantasy video games.
Most of the gamers I know have watched and really enjoyed ST. However, most of us are in our 40s and started playing RPGs decades before ST existed. And there are several people I know, including my wife, who really like ST but aren't into TTRPGs.
I do think that ST has almost certainly had a positive impact on the popularity of D&D, but I suspect that it is relatively minor. In an alternate universe where ST never existed, I don't think the number of people playing D&D would be dramatically different (although I do expect that overall public awareness probably would be significantly reduced).