Deadpool wasn't in the MCU before because it was made by FOX, so this is his first venture into the MCU since Disney acquired FOX. Multiversal stuff. Other than going into the multiverse like a couple projects before, the TVA is the perfect way to bring the FOX Marvel into the rest of the MCU.
Lol, yes, it's so confusing now as to what's canon and what's not! Either way, it's good to see Deadpool coming closer to the other Marvel franchises! He's "Marvel Jesus", after all! 😂