The documentation shows how to update a single work item via the Azure DevOps (Server) Rest API, but in the past, using the TFS client object model, one could send batch update / save requests to the TFS system that contained more than one work item.
Is this still possible with the Rest API and if so, how?
I recommend to you to use the SDK which is into the NuGet package Microsoft.TeamFoundationServer.Client so not rely directly on the Rest API as that is a wrapper of the API.
If you search for examples in order to use that SDK you can find them here, https://github.com/microsoft/azure-devops-dotnet-samples/tree/main/ClientLibrary/Samples
The method that I am using it is into the WorkItemTrackingHttpClient class method client.ExecuteBatchRequest(my list of requests);
