Why is it in the CTF game mode you “CANNOT” carry the FLAG in any vehicle in HALO INFINITE??? There is no setting for this in the CTF GAME MODE SETTINGS!!! 
You can Halo 2, Halo2A, Reach and Halo4 but you “CANNOT” in HALO INFINITE!! WHY?
I RUN BIG TEAM BATTLE MAPS ONLY!!
Here s pic from Halo 2A CTF Game Mode Settings for proof!:
https://ibb.co/s92PJBD
Peace! 
Try it with scripting within forge. Scripting seems to be 343s response to how terrible the custom games settings have been set up.
Well I don’t have Forge Right Now but is give it a try if we get forge. Not sure if you will be able to because of the “ANIMATIONS” when you grab the flag in a vehicle.
Example: when you get grab the flag and jump into a Ghost the flag will popup in the reae end of the ghost. That is how you carry the flag in a ghost. The same goes for other vehicles. Now if there was a way to show you have the flag in vehicle when your in a Banchee using the “FLAG ICON” while your in the vehicle that may work.
In the CTF game mode I set the setting to SHOW THE FLAG SET TO “ALWAYS” but you still got to be able to drive a vehicle with the flag. This really sucks that you can’t in the CTF Custom Game Settings in Halo Infinite!!!
I am a old school type person. "IF IT AIN’T BROKE DON’T FIX IT GEEZE!!!
Peace!