Today’s update for It Takes Two adds support for Steam Deck and game invites through the Steam friends list, and removes the need for the EA App launcher.
It most transactions, the 2 parties are the purchaser and the seller.
If you buy a game from Steam, using the steam launcher isn't a third-party launcher.
If you bought a game directly from EA, their launch isn't a third-party launcher.
If you bought the game from Steam, the EA launcher is third-party.
Reached out to EA to see if I could get my key transferred over. The answer was no, of course. But it’s still annoying that I get less for having bought sooner on their platform rather than waiting for it to be available on Steam.