Microsoft Graph; Create calendar event; how to set ICalUId so that later I can find the event via the ICalUId - powershell

Question

I am trying to create events via the MS Graph API (with Powershell but using the REST API).
So far I can create events without problems. All the properties I want to set are correctly set - except I don't seem to manage to set the IcalUId - as I cannot find such created events via
"/users/$UPNofMBX/calendar/events?`$filter=iCalUId eq '$appointment_UID'"
($Appointment_UID = the desired identifier for later finding the event - It is coming from an external - commercial solution)
If I import via Outlook an ICS file with a specific value in the "UID:" field, the above Graph query finds the event which carries the searched for value in the ICalUId field.
If I set it at creation time via graph with the below body, the above search query line does not find the event.
The body of the REST call looks like this:
$Body = #"
{
"subject": "$appointment_Subject",
"iCalUId": "$appointment_uid",
"body": {
"contentType": "HTML",
"content": "$appointment_Body"
},
"start": {
"dateTime": "$appointment_Time_Start",
"timeZone": "Europe/Berlin"
},
"end": {
"dateTime": "$appointment_Time_End",
"timeZone": "Europe/Berlin"
},
"location":{
"displayName":"$appointment_Location"
},
"attendees": [
{
"emailAddress": {
"address":"$UPNofMBX",
"name": "Ressource"
},
"type": "required"
}
],
"allowNewTimeProposals": false,
"transactionId":"$(New-Guid)"
}
Unfortunately, in none of the examples # Microsoft is the use of the ICalId explained when creating an event. Also I didn't find any examples on the net.
Hint: If I use Microsoft.Exchange.WebServices.Data within a C# app, I can set the iCalUId.
The goal is to set a reference UID / ID / anything in the to-be-created event so that I can find this event later via this reference in order to update or delete it. The only reference information I have is the UID (iCalUId) from an (update/delete) ICS file from the external commercial solution.
I would prefer to not build a translation table between the UIDs from the commercial solution when they arrive via ICS and the IDs of the newly created events when they are given back in the REST call # creation time so I can find them later if necessary.
Any insight what I am doing wrong or a solution is greatly appreciated.