If I recall correctly, there used to be an option to get a command prompt under System -> Diagnostics -> Command Prompt. That menu doesn't exist anymore. Searching for 'command prompt', 'console', or 'shell' in the search bar comes up empty.
Is the feature gone?
Yes, a long time ago.
For everything else there's ssh or console access
Almost exactly ten years? https://github.com/opnsense/core/commit/f2a21ac446
Cheers,
Franco