Oooo!! I know this one.
Apple CarPlay uses Bluetooth to initiate the connection between your phone and the car. During that initiation process, a private Wifi network is created between your car and your phone, and the credentials for that Wifi network is passed over the Bluetooth connection. Once established, the private Wifi network it creates is what is used to communicate between the car and the phone.
Because the Wifi radio is busy running CarPlay, it cannot be used for the AT&T hotspot. Some Ford vehicles can do both at the same time (not sure about the Bronco to be honest), but it's a mute point anyway because the iPhone is only capable of doing one or the other.
Theoretically if you plug in your phone via USB, it will switch over to using wired CarPlay over USB. And once it does, that you should regain access to the hotspot feature. The switch is supposed to be seamless, but in my experience sometimes it's a bit stubborn and you have to toggle on/off Airplane mode on your phone force it to switch over.
2022 4dr Badlands, 2.3L Manual, Mid pkg
YouTube: youtube.com/@ragnarkon
Instagram: @ragnar.kon