How to monitor Mongo databases and Cloud servers?
As per MongoDB documentation here Starting in version 4.0, MongoDB (Community Edition) offers free Cloud monitoring for standalones and replica sets.

Free monitoring provides information about your deployment, including:


Operation Execution Times
Memory Usage
CPU Usage
Operation Counts


By default, you can enable/disable free monitoring during runtime using db.enableFreeMonitoring() and db.disableFreeMonitoring().

You can also enable or disable free monitoring during mongod startup using either:


the configuration file setting cloud.monitoring.free.state
or
the command-line option --enableFreeMonitoring


Once you enable free monitoring, it remains enabled until you disable it.