conda is installed but your shell has not been told about it
The installer adds an initialisation block to your shell profile, and that block only takes effect in a new shell. If you skipped the init step, or you use a shell the installer did not configure (zsh vs bash), the command is not on your PATH.
Run the installer's init once — ~/miniconda3/bin/conda init zsh (or bash) — then open a new terminal. Editing PATH by hand also works but skips the shell functions conda activate needs.