How do I enable Maintenance mode (to display a maintenance message in Matomo, and disable tracking) prior to updates? FAQ - Analytics Platform - Matomo

You can define a setting in your config/config.ini.php file as explained in this FAQ.

Next FAQ: How do I upgrade a large Matomo instance without losing any tracking data? (no Tracking API downtime)

Previous FAQ: I would like to test early beta and RC releases, how do I enable automatic updates to use these development versions?