As halftrainedharry suggests, it’s most likely that a widget is causing the problem. I’d recommend removing widgets from that dashboard one at a time to see if you can figure out which one it is. Start with the ones not installed by MODX in a fresh install.
Thanks for the idea bobray to check the widgets on the dashboard. The error only seemed to occur on the dashboard page. Was using the default set of dashboards. Managed to determine the error to only occur if I have “configuration check” widget switched on. Removing that from the default set removes the error.
Using PHP 7.4 with PHP-FPM
That’s really strange. Almost everyone has the same setup when they install MODX and I’ve never seen that error message reported. Do you have any plugins that would fire on any Manager events?
The cause would most likely be a line somewhere with one of these tags in it: