Graph Client Application[xx].PatchAsync not working as expected

hello dBarrettTP​ . I had the same issue (seems like a few weeks ago a change in Graph API introduced this issue). We were able to identify it quickly enough thanks to our AT team but the issue is still there. As a hint, I was able to fix it by setting any value to the IdentifierUris property when call the PostAsync() to create the app registration. E.g.

IdentifierUris = new List<string> { $"https://{_graphApiOptions.TenantName}" }

Once you get the success response, then you can call the PatchAsync() the same way you are doing right now and it should work fine. Please, let me know if this worked for you, thanks.

PS: We're using Microsoft.Graph v5.105.0