$apply aggregation on nested collection not working or combined with Param $expand also not functioning

Please check the repository (Sample Project) : https://github.com/padhumailin/ODataV8Demo

Parent entity Accounts has a collection property LinkedAccounts Entity, I need to apply aggregation on collection property

filter on collection is working:
http://localhost:34987/api/accounts?$filter=LinkedAccounts/any(a:a/LinkedAccountName eq 'Loan1')

aggregation on parent entity also working:
http://localhost:34987/api/accounts?$apply=groupby((AccountType), aggregate($count as total))

aggregation on collection property not working
http://localhost:34987/api/accounts?$apply=groupby((LinkedAccounts/ParentId),%20aggregate($count%20as%20OrderCount))

http://localhost:34987/api/accounts?$expand=LinkedAccounts($apply=groupby((ParentId),%20aggregate($count%20as%20OrderCount)))

ERROR:
{"error":{"code":"","message":"The query specified in the URI is not valid. The parent value for a property access of a property 'ParentId' is not a single value. Property access can only be applied to a single value.","details":[],"innererror":{"message":"The parent value for a property access of a property 'ParentId' is not a single value. Property access can only be applied to a single value.","type":"Microsoft.OData.ODataException"

Expected Result:
[{"ParentId":"1","total":3},{"ParentId":"2","total":3},,{"ParentId":"3","total":3}]

Any suggestion on how to implement the EDM model or any diiferent way to write odata parameters to acheive

Environment:
Net 6
OData 8.0.4