Patch(
YourSharePointList,
Defaults(YourSharePointList),
{
PersonOrGroupColumn: {
'@odata.type': "#Microsoft.Azure.Connectors.SharePoint.SPListExpandedUser",
Claims: "i:0#.f|membership|user@externaldomain.com",
DisplayName: "User Name",
Email: "user@externaldomain.com"
}
}
)