honkoma/docs/static_dir.md

Static Directory

Static frontend files are shipped in priv/static/ and tracked by version control in this repository. If you want to overwrite or update these without the possibility of merge conflicts, you can write your custom versions to instance/static/.

config :pleroma, :instance,
  static_dir: "instance/static/",

You can overwrite this value in your configuration to use a different static instance directory.

robots.txt

By default, the robots.txt that ships in priv/static/ is permissive. It allows well-behaved search engines to index all of your instance's URIs.

If you want to generate a restrictive robots.txt, you can run the following mix task. The generated robots.txt will be written in your instance static directory.

mix pleroma.robots_txt disallow_all