NoWayOut In the US, all the three big carriers do it.
My carrier is Verizon. They write:
Many of our monthly phone plans and certain prepaid plans let you use 5G Ultra Wideband, 5G and 4G LTE Mobile Hotspot on capable devices for no additional monthly charge.
I looked at my "plan features" page and it says only:
Personal Hotspot
Use your shared data to turn your smartphone into a Wi-Fi connection for your other devices.
So it's not clear to me that I have a tethering quota. They may have some plans with tethering limits, but that may be avoidable - on Verizon and maybe also on other carriers.