Insight plugin can only be disabled using REST API using the following command and payload:

PUT /rest/plugins/1.0/com.riadalabs.jira.plugins.insight-key

Header:

Content-Type: application/vnd.atl.plugins.plugin+json

Body:

{
    "enabled": false
}

Insight plugin version 9.1.x is installed along with the Jira Service Management application and can be found on the Manage apps page, under User-installed apps.

The Disable and Uninstall buttons are both available, however, attempting to disable/uninstall the Insight plugin will uninstall Jira Service Management application and hence, it's not recommended to disable/uninstall Insight even though it is not currently in use.

Insight plugin version 9.1.x or above is bundled and can be found via Manage apps > Application components.

Insight cannot be disabled/uninstalled separately without disabling/uninstalling the Jira Service Management application.

Insight version 9.0.x is installed along with the Jira Service Management application, it is listed under User-installed apps. 

If Insight is not intended to be used, it can be disabled as well as uninstalled via the Universal Plugin Manager (UPM) by clicking on the Disable or Uninstall button available as shown below.

Insight version 9.0.x is part of Jira Service Management application and hence, it cannot be disabled on the Manage apps page.

It can only be disabled using REST API using the following command and payload:

As the new server license sales ended on February 2, 2021, the Insight app/capabilities is no longer included in Jira Service Management Server and hence, it's not possible to browse for Insight and install it without leaving Jira.

To install Insight,

1. Download the OBR file from Atlassian Marketplace .
2. Install Insight from the downloaded file as per  Install an app from a file .

If Insight is not intended to be used, it can be disabled/uninstalled via the Universal Plugin Manager (UPM).

Yes

Insight app version below 8.x can be browsed and installed from Atlassian Marketplace directly via the Universal Plugin Manager (UPM).

Insight plugin can be managed under User-installed apps list.