Hi @Reham Eltamimi ,
Each group has a shared calendar where you and every member of your group can schedule, edit, and see upcoming events.
So I don't think we could make the site user without the group member or group owner to see the group calendar in Site main page.
This means it's necessary to "Add members to group", rather than just sharing the site as visitor only.
More information:
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.