Hello john john,
Thanks for reaching out!
Currently using Microsoft Graph API, you can either get site permission and get drive item permissions and it is not possible to break the permission inheritance for a SharePoint custom list item and get all the permission assignments. You can send a sharing invitation to user using Microsoft Graph API.
Using SharePoint REST APIs you can get permissions for a site, list, library, item as well.
https://domain.sharepoint.com/_api/web/lists/GetByTitle('{listTitle}')/RoleAssignments?$expand=Member
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