Well, after trying so many things over the last several months, I?ve decided to ask for help on this:
In the USB arsenal section, the text fields are all grayed out.

idVendor, idProduct, manufacturer, product, and serialnumber fields are all disabled. I can?t type in any of them. Also the button to ?save config to database? is also disabled and grayed out.

This is on a OnePlus 7 Pro, with the latest international OS version, magisk 20.4, and NetHunter 2020.3, upgraded from 2020.2. I think I?m going to try directly downloading 2020.3, and installing again from TWRP, but I doubt it?ll help. FWIW: I have never been able to get it to work.