Hi @rbarrameda ,
Do you want to update group by not using combo box?
The formulas to update person and group are different.
The formula to update person:
{'@odata.type':"#Microsoft.Azure.Connectors.SharePoint.SPListExpandedUser",
Claims:"i:0#.f|membership|" & Emailaddress,
Department:"",
DisplayName:FullName,
Email:Emailaddress,
JobTitle:"",
Picture:""
The formula to update group:
{'@odata.type':"#Microsoft.Azure.Connectors.SharePoint.SPListExpandedUser",
Claims:"c:0o.c|federateddirectoryclaimprovider|group objectID",
Department:"",
DisplayName:"groupname Members",
Email:"group email address",
JobTitle:"",
Picture:""
}
You could find your group objectID in adure AD admin center.

I've made a similar test, here's the formula that I use:
{'@odata.type':"#Microsoft.Azure.Connectors.SharePoint.SPListExpandedUser",
Claims:"c:0o.c|federateddirectoryclaimprovider|17347cb7-aaef-4361-915e-7d4.....",
Department:"",
DisplayName:"test126126 Members",
Email:"test126126@.....com",
JobTitle:"",
Picture:""
}
Best regards,