USB tethering much slower than WiFi tethering

Question

In my area, my home Internet will often go down due to storms. At these times, I need to tether using my 4G LTE mobile phone, which gets decent speeds of around 10 Mb/s download and similar for upload.

While USB tethering, my download speeds on my laptop are constantly very slow, typically around 0.2 to 0.3 Mb/s. However, if I tether via Wifi my download speeds are about the same as the speeds on my phone itself (around 10 Mb/s).

I have compared speeds hundreds of time using SpeedTest.net. On my phone I use the SpeedTest.net Android app.

I have been with my mobile provider for many years; this problem started 1.5 years ago and nobody at the mobile provider has been able to help. The problem happens with all the phones I have owned during this time (several LG and Samsung devices) with all the different computers (both laptops and desktops) and the pattern is always the same.

How can I find out if this is throttling by the carrier in response to USB tethering or if this is a problem with my computer configuration related to USB tethering. Most of my computers run Linux and there isn't really much configuration needed because USB tethering "just works". However, I suspect there may be configuration options I could investigate but which I am unaware of.