brew install cmctl

go install github.com/cert-manager/cmctl/v2@latest

OS=$(uname -s | tr A-Z a-z); ARCH=$(uname -m | sed 's/x86_64/amd64/' | sed 's/aarch64/arm64/'); curl -fsSL -o cmctl https://github.com/cert-manager/cmctl/releases/latest/download/cmctl_${OS}_${ARCH}
chmod +x cmctl
sudo mv cmctl /usr/local/bin
# or `sudo mv cmctl /usr/local/bin/kubectl-cert_manager` to use `kubectl cert-manager` instead.

$ cmctl completion --help
# or `kubectl cert-manager completion --help`
...
Available Commands:
  bash        Generate cert-manager CLI scripts for a Bash shell
  fish        Generate cert-manager CLI scripts for a Fish shell
  powershell  Generate cert-manager CLI scripts for a PowerShell shell
  zsh         Generation cert-manager CLI scripts for a ZSH shell
$ cmctl completion bash --help
To load completions:
Bash:
  $ source <(cmctl completion bash)
  # To load completions for each session, execute once:
  # Linux:
  $ cmctl completion bash > /etc/bash_completion.d/cmctl
  # macOS:
  $ cmctl completion bash > /usr/local/etc/bash_completion.d/cmctl
...