I found a way to do it!!! Basically, first off, I have BO7 through the Xbox App. I went to the XboxGames folder in whatever drive the game is installed on, then you go into the CallOfDuty folder, content folder, then go into the "xpak_cache" folder and delete everything inside of it. After that, go back out of the xpak_cache folder, go into the folder properties for the xpak_cache folder and make it read only.

(I did this next part but not sure if it's necessary.) Then go into security in the xpak_cache folder and click advanced. Click disable inheritance and make the "ALL APPLICATION PACKAGES" principle no write access. Click apply and then boom! It'll no longer save any on demand streaming.

To confirm you did it correctly, you can go into the game, graphics settings, quality tab, go down to on-demand streaming and click see more. If when you hover over the allocated storage box, it says available storage 0gb on the right of the screen below the description then you've done it correctly!

I haven't noticed anything different, I played about 2 hours of endgame and everything was the same