Maybe a stupid question but for using

ruff

for example if I just want to use it but I don't need any additional configuration I just need to add the backend, I don't need a config section?

I don't know the details of

ruff

but I have a number of backends enabled with no corresponding configuration section

config sections are generally for overrides or if you want to do something specific. All the linters/formatters especially should typically look at your normal config files (pyproject.toml) and whatnot. That's not always perfect, but it's usually better (to use the standard configuration files, instead of pants.toml) if you want to have a similar experience whether you run with pants or not

I have used pants for formatting only on some projects by adding pants.toml and one BUILD file with a python_source sowning all the python files in the repo. This is very easy to set up to get formatters and fixers "for free".