Here's what happened to me (FP5):
USB tethering WORKED until February 22nd (2026), when I installed the candidate release (version 10).
Today I noticed it no longer worked.
I tried switching to the "daily" release channel: I installed "1007" and it still doesn't work.
Then I switched to the stable version ("3") and it still doesn't work.
In the settings, when I log out and log back in, it switches from "tethering" to "charging only"... but sometimes it stays on tethering (but nothing changes).
Even using the UT Tweak Tool, things don't change.
It seems that, installing the new RC, something got corrupted and now it no longer works with any release (but it worked until February 22nd, at least with the previous RC channel, which I was on since the switch to "24 noble").
NB: Connecting a PC, decoder, etc. to the GSM (handy) network via (handy) Wi-Fi/Wlan -> works out of the box... only via USB cable no longer works...