If it helps EE I believe is something like 600GB, it used to be more.  But I use that most months (work from home on 5G with EE) so everything is going through.  Streaming, work, gaming, calls, etc.  TBH though streaming isn't that intensive.  I think Netflix at 1080p is 2-3Mbps.  Never had any problems with EE over the years.  I think if they see mega high usage consistantly they get in touch and look to shift you to a business plan.  
This is from their unlimited pay monthly T&Cs.
"If you regularly tether 12 or more devices, we will consider this non-personal use and have the right to move you to a more suitable plan. We will consider usage above 600GB per month to be non-personal use and have the right to apply traffic management controls to deprioritise your mobile traffic during busy periods, or to move you to a business plan."
	
		
			
		
		
	
				
			This is from their unlimited pay monthly T&Cs.
"If you regularly tether 12 or more devices, we will consider this non-personal use and have the right to move you to a more suitable plan. We will consider usage above 600GB per month to be non-personal use and have the right to apply traffic management controls to deprioritise your mobile traffic during busy periods, or to move you to a business plan."
 
	 
  
 
		 
 
		 
 
		 
 
		