Adding webparts on O365 Modern site page

 Add-PnPClientSideWebPart -Page "" -Component "" -WebPartProperties ""

Explanation of Parameters

Page - Accepts String

Component - Accepts String

WebPartProperties - Accepts JSON Object

JSON Object can be as simple as: 

$jsonObj = @"

{

"Property1": "value",

"Property2": "value"

}

"@

Sometimes, one can easily add webparts from the userinterface, and hard to identify the property names to configure the webpart. In those scenarios, use this:

$page = Get-PnPClientSidePage -Identity ""    

Explanation of parameters

Identity - Accepts String (example: home.aspx)

$webpart = $page.Controls | ? {$_.InstanceId -eq "GUID string"}  

Explanation of parameters

GUID String can be accessed from the Source control of the page (from UI)

$webpart.PropertiesJson

Will reveal the properties in JSON Format, that can be used as is in the First command above to add webpart on the page.

Source: 

Self, and

Working with modern client-side pages using PnP PowerShell