The following construct is flagged as invalid (context "inputs" is not allowed here. no context is available here.):

uses: docker://<image-name>:latest
with:
  entrypoint: /bin/sh
  args: >
    --arg "${{ inputs.arg }}"

Though based on https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/accessing-contextual-information-about-workflow-runs#context-availability this is valid, and equally this works fine.