Hi Amey,
Insight is a built-in component of Dynamics Marketing.
Unlike other common components, it won't display in list for us to select.
The "Insights" field you added is actually a text field, which is not the real Insights widget. (You can find the field in Customization > Contact > Fields.)
A workaround is that by creating a new form in classic UI, the component will be available by default, then customize the form with layout you want.

Not sure whether it is an issue: after I saved and published the custom form, it didn't display in form selector, thus I took further steps to make it works.
1. Open Marketing app in App Designer, enable the form.

2. Set the custom form as the first item, then publish all customization.

Result:
Now my custom form has appeared in selector, and Insights component is also there.

Regards,
Clofly