Regarding installing with Azure CosmosDB mongodb I get the following error. I have a serverless setup fixed to max 20GB but that should suffice.

Setup failed: Command create failed: Error=13, Details='Response status code does not indicate success: Forbidden (403); Substatus: 3090; ActivityId: af6dc2f4-8006-40a4-ba7c-c39e8c65337c; Reason: (Message: {"Errors":["Storage quota for 'Collection' exceeded."]} ActivityId: af6dc2f4-8006-40a4-ba7c-c39e8c65337c, Request URI: /apps/c0e280a7-7474-4a48-a873-2797e073325c/services/6172d88b-02f3-482e-a1e9-c5c41b454887/partitions/0ba22776-313b-4997-8efe-2bf7261d9b40/replicas/132962301019769311p, RequestStats: , SDK: Microsoft.Azure.Documents.Common/2.14.0, Microsoft.Azure.Cosmos.Tracing.TraceData.ClientSideRequestStatisticsTraceDatum, Windows/10.0.19041 cosmos-netstandard-sdk/3.18.0);.

Trying with the local Cosmos DB emulator I get the following error which doesnt give me much to work with either.
"System.FormatException: The size of the message is invalid." This looks interesting but not sure how to figure out more about it?

A timeout occurred after 30000ms selecting a server using CompositeServerSelector{ Selectors = MongoDB.Driver.MongoClient+AreSessionsSupportedServerSelector, LatencyLimitingServerSelector{ AllowedLatencyRange = 00:00:00.0150000 }, OperationsCountServerSelector }. Client view of cluster state is { ClusterId : "8", Type : "Unknown", State : "Disconnected", Servers : [{ ServerId: "{ ClusterId : 8, EndPoint : "Unspecified/localhost:8081" }", EndPoint: "Unspecified/localhost:8081", ReasonChanged: "Heartbeat", State: "Disconnected", ServerVersion: , TopologyVersion: , Type: "Unknown", HeartbeatException: "MongoDB.Driver.MongoConnectionException: An exception occurred while opening a connection to the server. ---> MongoDB.Driver.MongoConnectionException: An exception occurred while receiving a message from the server. ---> System.FormatException: The size of the message is invalid. at MongoDB.Driver.Core.Connections.BinaryConnection.EnsureMessageSizeIsValid(Int32 messageSize) at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveBuffer(CancellationToken cancellationToken) --- End of inner exception stack trace --- at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveBuffer(CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveBuffer(Int32 responseTo, CancellationToken cancellationToken) --- End of stack trace from previous location --- at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveBuffer(Int32 responseTo, CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.BinaryConnection.ReceiveMessage(Int32 responseTo, IMessageEncoderSelector encoderSelector, MessageEncoderSettings messageEncoderSettings, CancellationToken cancellationToken) at MongoDB.Driver.Core.WireProtocol.CommandUsingQueryMessageWireProtocol`1.Execute(IConnection connection, CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.HelloHelper.GetResult(IConnection connection, CommandWireProtocol`1 helloProtocol, CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.ConnectionInitializer.SendHello(IConnection connection, CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.BinaryConnection.OpenHelper(CancellationToken cancellationToken) --- End of inner exception stack trace --- at MongoDB.Driver.Core.Connections.BinaryConnection.OpenHelper(CancellationToken cancellationToken) at MongoDB.Driver.Core.Connections.BinaryConnection.Open(CancellationToken cancellationToken) at MongoDB.Driver.Core.Servers.ServerMonitor.InitializeConnection(CancellationToken cancellationToken) at MongoDB.Driver.Core.Servers.ServerMonitor.Heartbeat(CancellationToken cancellationToken)", LastHeartbeatTimestamp: "2022-05-06T10:57:47.7089287Z", LastUpdateTimestamp: "2022-05-06T10:57:47.7089290Z" }] }.

Ok, by some reason serverless doesnt work. Setting the Azure Cosmos Mongo DB to provisioned will work.
Next error is the sitemap can't be fetched due to
MongoCommandException: Command aggregate failed: Error=2, Details='Response status code does not indicate success: BadRequest (400); Substatus: 0; ActivityId: f9f42b1f-e596-4fbc-a588-fd428b485ee9; Reason: (Response status code does not indicate success: BadRequest (400); Substatus: 0; ActivityId: f9f42b1f-e596-4fbc-a588-fd428b485ee9; Reason: (Response status code does not indicate success: BadRequest (400); Substatus: 0; ActivityId: f9f42b1f-e596-4fbc-a588-fd428b485ee9; Reason: (Message: {"Errors":["The index path corresponding to the specified order-by item is excluded."]} ActivityId: f9f42b1f-e596-4fbc-a588-fd428b485ee9, Request URI: /apps/1fd53e80-bf7d-4d45-8d9f-a6bb55f87347/services/fb1b35ae-8a9d-4090-ae85-a35363371e82/partitions/019aee3f-c6fc-44da-814a-b04cf3e2cdbd/replicas/132963177110751088s/, RequestStats: Microsoft.Azure.Cosmos.Tracing.TraceData.ClientSideRequestStatisticsTraceDatum, SDK: Windows/10.0.19041 cosmos-netstandard-sdk/3.18.0);););.

Moving forward.

AsBsonDocument = {{ "aggregate" : "AdminSiteMap", "pipeline" : [{ "$sort" : { "DisplayOrder" : 1 } }], "cursor" : { } }}

Unable to cast object of type 'MongoDB.Bson.BsonDocument' to type 'MongoDB.Bson.BsonDateTime'.

Looking at the inner exception of e in the modified code here.

var siteMap = new SiteMap(adminSiteMapService, permissionService);
    try
    {
        await siteMap.Load();
    }
    catch (Exception e)
    {
        var test = e;
    }

Anyone have an idea of if this is me who should be fixing this or if GrandNode simply just isnt compatible with Azure CosnmosDB MongoDB?

Something about the OrderBy value missing or not being correct. Changed to this and it "works" now.

public virtual async Task<IList<AdminSiteMap>> GetSiteMap()
        {
            return await _cacheBase.GetAsync($"ADMIN_SITEMAP", async () =>
            {
                var query = from c in _adminSiteMapRepository.Table
                            select c;

                var list = query.ToList();
                if (list.Any())
                    return list;
                else
                    return await Task.FromResult(StandardAdminSiteMap.SiteMap.OrderBy(x=>x.DisplayOrder).ToList());
            });
        }

Serverless didnt work because there is a restriction on 100 containers per db and GrandNode is using something like 140(?).
Is there a way some of these could be grouped? As of now a basic database for grandnode in Azure is 50euros per day with provisioned 400RU's.

Just an FYI. Azure team got back and will raise number of containers for serverless to work. To get that one need to create a support ticket asking for more collections in the Cosmos MongoDB db.