I stated “limited protection”, as there are also systems with multiple USB controllers available, like desktop computers or via PCIe extension cards. This allows to mitigate damage with proper separation of critical USB devices like keyboards.
USB keyloggers are not without dangers in Qubes OS either. We simply need a keyboard to administer our computer (“dom0”), hence even the Qubes OS USB model/qube naturally allows typing everywhere. If I am not mistaken, there are USBGuard policies in place to prohibit unknown USB devices trying to act as additional keyboard, but this is not Qubes OS-specific protection. Optimally you got multiple USB controllers and are configuring a separate USB qube/controller just for the keyboard.
In summary, for ease of use and to not bother about every circumstance, I just would plug the USB device into a separate system, like an old Raspberry Pi, and copy data from there.
// Edit:
I was referring to OP’s case, where you simply need to plug in an unknown or untrusted USB stick into your computer. If threat model involves physical access of malicious actors, that e.g. can unplug your keyboard and plug in another stick, these protections of course are not sufficient.
This is not true by default, you have to specifically configure the option to allow USB input devices. On laptops where the built-in inputs are not connected via USB, for example, there’s no reason why USB input devices need to be treated any differently than any other USB device.
Good point. Most of the notebooks use PS/2 internally for keyboard according to their docs (some still USB). So I guess that’ll give them an edge in terms of security over USB keyboards.