Thanks for getting in touch! I'm sorry to hear you're hitting this issue when trying to disable your step. Recently we've fixed an issue to prevent disabling a step when this step is used by Automatic Release Creation. Your screenshots show that ARC isn't configured, so this is a bit curious.
Are you able to successfully disable other steps in the same project?
If so, could you check via the API if this project has ARC somehow incorrectly defined? You can reference the project ID at OctoURL/api/projects, and view this specific project at OctoURL/api/projects/projects-ID, where the ReleaseCreationStrategy would be populated.