On Sharepoint Online we have two different sites.
First site is created throught Office 365 Group. So, we created Office 365 group and sharepont site is created automatically with various web parts available (Planner, Connectors,...)
Second site is "regular" team site and in that team site we are missing those webparts. Please check images.
In apps there are no those apps. How to add all webparts from first site to team site?
Group site web parts
Team site web parts
Unfortunately, these connector webparts are only available in O365 group backed team sites and not in communication site or team site (without associated O365 group).
So, you wont be able to add these apps in your site unless its backed by O365 group.
References -
Use SharePoint web parts to showcase data from inside and outside Office 365
There is a user voice open for this as well. You can upvote it and hope MS listens, but at the moment its not possible in your scenario.
