This usually occurs because Emacs doesn’t have the same environment
variables as your shell. Try installing and configuring
https://github.com/purcell/exec-path-from-shell. By default it
synchronizes $PATH, which helps Magit find the same git as the one you
are using on the shell.
If SOMETHING is "passphrase caching with gpg-agent for commit and/or
tag signing", then you’ll also need to synchronize $GPG_AGENT_INFO.