Currently (8th june 2022) working solution on Xbox: with the game closed, go to the console network settings and disconnect. Then start MW, a message warning you that internet is needed will pop-up, just press disconnect. Then start Local multiplayer and you will see clearly that they let you add the 2nd controller.
We keep bouncing back to COD MW2019 as well, worried they'll take the servers down soon. The aesthetic updates are all well and good, but they need to get on board with the gameplay. Very few couples or siblings will buy 2 TVs, 2 games, and 2 consoles just to play. 90% of the Playlist right now are anit-split-screen.
rDH4Is.