Can I not manually trigger a DAG on a deployment that runs on LocalExecutor?

Correct - this is expected behavior, as the Trigger DAG button from the Airflow UI actually only works when using the Celery Executor. When you’re developing locally, the Local Executor is used (the decision to not offer Celery locally was intentional so as to keep the resource footprint lightweight).

As a workaround for development, we’d recommend setting the schedule_interval to @once and turning on the DAG to execute it. It will only run one time and if you need to run it again, clearing (not “retry-ing”) all the tasks will cause it to restart.