I was wondering how T-Mobile detects hotspot usage and hadn't been able to evade the detection using the various online tutorials and the advice given here.
If I understand correctly, they check the TTL counter of the passing data packets (that your internet traffic is wrapped in). If there are extra "routers" (like a wifi hotspot) on the way from cell service router to the target device, the TTL will be lower, than it would have been if the packets originated from the smartphone, since when passing each router the TTL value get's decremented by one.
So to bypass this, you need to change (increment by 1) the default initial TTL value (64 on MacOS) on your connected device - i.e. your MacBook, so the cell service doesn't notice the difference from the stock android initial TTL (which is 64, as I understand) once the packet reaches your service provider:
sudo sysctl net.inet.ip.ttl=65
Haven't tried doing that myself, though.