Is this how 5G Hotspots work on T-Mobile ?

I currently have an outage of my regular internet provider (AT&T) and a friend let me use his T-Mobile 5G Hotspot. It was working great at 10mb/sec for a day and a half, then it slowed down to .014 Mb/sec. I checked the router and it said '10gb monthly limit has been reached and will reduce speed until the next billing cycle' . I sort of expected an eventual slowdown ( maybe 4G )  but  to 100kb/sec makes the internet almost un-useable ( it took 2 min for this page to load ). The first 1½  days almost had me changing but if this is the way it is going to be I am going to avoid T-Mobile.

 Is this the way 5G hotspots work on T-Mobile ?