Redox OS, a cool experimental operating system written in Rust, doesn't have USB support at runtime, which means it's very difficult to install and use on a typical physical computer.

Adding USB support does not appear in their "Development Priorities for 2023/2024", but they do indicate a focus on improved support for real hardware, and in their FAQ under "Hardware Interfaces", they list "(USB soon)" (however, it's said this for at least several months).