NextCloud 27.0.0. Use system cron service to call the cron.php file every 5 minutes. Recommended for all instances. The cron.php needs to be executed by the system user "www-data".

Above is the entire warning message in the Administrative – Overview section of NextCloud.

Select the correct radio button within nextcloud administration.

This eliminates the entire Cron problem without any additional configuration.

The Ajax service runs the job every time a user accesses a page of NextCloud.