Big Sur 11.2.2: Operation not permitted although Iterm and Terminal have Full disk access
You are supposed to install third party software to /usr/local/bin. This is the default used by most Unix installers and build systems.
(Alternative directories in the root for example under /opt can be used if you have fu;ll control of how the software is built)
The folder /usr/bin is protected by SIP as it contains software supplied by Apple as part of macOS (In Big Sur this is even more difficult if at all possible to alter)