Hope you are trying to monitor the .NET application hosted on Azure app service.
The APM Insight .NET Agent extension in Azure app service will add this environment variable COMPLus_LoaderOptimization in the .NET application hosted on Azure app service. This helps the .NET agent assembly to be loaded into the application properly. It will be added automatically through the applicationHost.xdt file, when you add APM Insight extension in your application.
If you face any problem with monitoring the .NET application in Azure app service, generate the diagnostic zip file from the azure app service and send it to email@example.com
Kindly refer the below doc to generate the diagnostic zip file from azure app service extensions.
APM Insight .NET Agent Team