I must say I am a little confused as you what you are referring to.
Tethering is a standard feature in Android since - at least v5 I think.
The carrier cannot possibly know if you are using tethering as this should be completely transparent - handled by the phone internally - but if they can and if they do - they are violating basic privacy rules as they should not monitor in any way what you are using your phone for.
You keep saying hot spot - but what are you referring to? Are you referring to the possibility of sharing your phones internet connection using WiFi or are you referring to your carriers internet connection?
Where I live - in Denmark - there is no restriction on what you can use your data plan for - data is data - so to speak - and what the data is used for is of no concern to the carrier - only thing is the amount of data transferred.