WebApi Unbound actions and functions are not called when custom routing is switched on

A unbound function is implemented with an "ODataRoute" Attribute, for example "[ODataRoute("MigrateFirebaseToMssql")]"
In the startup.cs file, default routing conventions are created ("ODataRoutingConventions.CreateDefault()")
an odata service route is created with these default conventions ("oRouteBilder.MapODataServiceRoute("odata", "", GetEdmModel(), new DefaultODataPathHandler(), oConventions, new DefaultODataBatchHandler());") -after these lines, the unbound function with attribute routing not callable anymore

Actual result

404 Error Result

Reproduce steps

Startup.cs

       oApp.UseMvc(oRouteBilder =>
            {
                // Create the default collection of built-in conventions.
                var oConventions = ODataRoutingConventions.CreateDefault();
                oRouteBilder.SetTimeZoneInfo(TimeZoneInfo.Local);
                oRouteBilder.Select().Filter().Count().MaxTop(null).Expand().OrderBy();
                oRouteBilder.MapODataServiceRoute("odata", "", GetEdmModel(), new DefaultODataPathHandler(), oConventions, new DefaultODataBatchHandler());
                oRouteBilder.EnableDependencyInjection();
            });

UnboundFunctionController.cs

[HttpGet]
 [ODataRoute("MigrateFirebaseToMssql")]
 public async Task<IActionResult> MigrateFirebaseToMssqlAsync()
        {
            return Ok(true);
        }