where was the top secret youtube event

The most likely answer is Raven Rock Mountain Complex in Pennsylvania, which reports linked to a secret-filming YouTube channel and described as a top-secret underground Pentagon facility.

What that means

The coverage says the accused YouTuber was tied to drone footage over restricted airspace above Raven Rock Mountain Complex.
That is the clearest public location connected to the “top secret YouTube” story in the search results.

Why there is uncertainty

Your wording could also refer to a different “top secret YouTube event” that isn’t uniquely identified here. The available public references point to a secretive YouTube-related incident, not a widely named event with one fixed venue.

Public read

In plain terms, the “where” appears to be the Raven Rock Mountain Complex area near the Maryland–Pennsylvania border.