I have to query the SharePoint group (not person or group column within the list ) and add users and grant permissions to that group through workflow.
How to add user to SharePoint group through workflow as every time the user list gets changed on item creation.
I have created this group Project Team manually.
If you are using Nintex for SharePoint on-premise, there is no action to add a user to SharePoint group, "Add user to a AD group" allows you to add to AD, not to SharePoint group.
But you can try using web service action (works for 2013, 2016 and 2019), here is the link
If you are using Nitex for SharePoint Online, you can use action, "Office 365 Add User to Group" action.