You can set parsing_processes from airflow > 2.0.0
# The scheduler can run multiple processes in parallel to parse dags.
# This defines how many processes will run.
#
# Variable: AIRFLOW__SCHEDULER__PARSING_PROCESSES
#
parsing_processes = 2
Source: https://airflow.apache.org/docs/apache-airflow/stable/configurations-ref.html#max-threads-deprecated