Hi, @bassem_abdalftah.
We don't control the loading and binding of the configuration values and can only access those provided via the IConfiguration instance passed into UseAllElasticApm. The Microsoft extension libraries (Microsoft.Extensions.Configuration, etc.) handle the loading of the values from the various configuration sources.
It doesn't look like this release-specific file is being loaded/used. Are you 100% certain that the app is running under the Release environment? At this point, I'd recommend double-checking your application environment and configuration first.
For example, if you add another key to the appsettings.Release.json file and attempt to access it from IConfiguration in your code, does it resolve the value from the appsettings.Release.json file? I suspect it won't.