YouTube has transformed itself from a place to watch funny cat videos, explorations of dance history, and Charlie biting fingers into one of the largest media companies in the world. But, in 2006, when Google bought YouTube for $1.65 billion , it was the early days of the online video boom. The staying power of the platform, which was founded just a year before the transaction, was still up in the air. Eighteen years later, investors in Google-parent Alphabet are now faced with a different, strangely positive kind of uncertainty. Could this sometimes overlooked business be worth as much as Netflix at nearly $400 billion? And now, where does it go from here? YouTube is just one of Alphabet’s many attention-grabbing assets. Waymo, its robotaxi venture, has been stealing…