Identity Server 4 can't find Certificate when deployed to Azure AppService

I have an asp.net core hosted blazor wasm application. I used the default template with authentication via Identity Server 4. When I test it locally in Release Mode it works as expected. But when I deploy to Azure AppService I get this exception:

    2020-05-08 07:45:50.244 +00:00 [ERR] An unhandled exception has occurred while executing the request.
Internal.Cryptography.CryptoThrowHelper+WindowsCryptographicException: The system cannot find the file specified.
   at System.Security.Cryptography.CngKey.Open(String keyName, CngProvider provider, CngKeyOpenOptions openOptions)
   at System.Security.Cryptography.CngKey.Open(String keyName, CngProvider provider)
   at Internal.Cryptography.Pal.CertificatePal.GetPrivateKey[T](Func`2 createCsp, Func`2 createCng)
   at Internal.Cryptography.Pal.CertificatePal.GetRSAPrivateKey()
   at System.Security.Cryptography.X509Certificates.X509Certificate2.get_PrivateKey()
   at Microsoft.IdentityModel.Tokens.X509SecurityKey.get_PrivateKey()
   at Microsoft.IdentityModel.Tokens.X509SecurityKey.get_PrivateKeyStatus()
   at Microsoft.IdentityModel.Tokens.AsymmetricSignatureProvider.FoundPrivateKey(SecurityKey key)
   at Microsoft.IdentityModel.Tokens.AsymmetricSignatureProvider..ctor(SecurityKey key, String algorithm, Boolean willCreateSignatures)
   at Microsoft.IdentityModel.Tokens.AsymmetricSignatureProvider..ctor(SecurityKey key, String algorithm, Boolean willCreateSignatures, CryptoProviderFactory cryptoProviderFactory)
   at Microsoft.IdentityModel.Tokens.CryptoProviderFactory.CreateSignatureProvider(SecurityKey key, String algorithm, Boolean willCreateSignatures)
   at Microsoft.IdentityModel.Tokens.CryptoProviderFactory.CreateForSigning(SecurityKey key, String algorithm)
   at Microsoft.IdentityModel.JsonWebTokens.JwtTokenUtilities.CreateEncodedSignature(String input, SigningCredentials signingCredentials)
   at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.WriteToken(SecurityToken token)
   at IdentityServer4.Services.DefaultTokenCreationService.CreateJwtAsync(JwtSecurityToken jwt)
   at IdentityServer4.Services.DefaultTokenCreationService.CreateTokenAsync(Token token)
   at IdentityServer4.Services.DefaultTokenService.CreateSecurityTokenAsync(Token token)
   at IdentityServer4.ResponseHandling.TokenResponseGenerator.CreateAccessTokenAsync(ValidatedTokenRequest request)
   at IdentityServer4.ResponseHandling.TokenResponseGenerator.ProcessAuthorizationCodeRequestAsync(TokenRequestValidationResult request)
   at IdentityServer4.ResponseHandling.TokenResponseGenerator.ProcessAsync(TokenRequestValidationResult request)
   at IdentityServer4.Endpoints.TokenEndpoint.ProcessTokenRequestAsync(HttpContext context)
   at IdentityServer4.Endpoints.TokenEndpoint.ProcessAsync(HttpContext context)
   at IdentityServer4.Hosting.IdentityServerMiddleware.Invoke(HttpContext context, IEndpointRouter router, IUserSession session, IEventService events)
   at IdentityServer4.Hosting.IdentityServerMiddleware.Invoke(HttpContext context, IEndpointRouter router, IUserSession session, IEventService events)
   at IdentityServer4.Hosting.MutualTlsTokenEndpointMiddleware.Invoke(HttpContext context, IAuthenticationSchemeProvider schemes)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at IdentityServer4.Hosting.BaseUrlMiddleware.Invoke(HttpContext context)
   at Serilog.AspNetCore.RequestLoggingMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Builder.Extensions.MapWhenMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>g__Awaited|6_0(ExceptionHandlerMiddleware middleware, HttpContext context, Task task)

In my appsettings I have this config:

  "IdentityServer": {
    "Clients": {
      "ApplySupportTool.Client": {
        "Profile": "IdentityServerSPA"
      }
    },
    "Key": {
      "Type": "File",
      "FilePath": "applysupporttool.pfx",
      "Password": "{Password}"
    }
  }

And in my Startup.cs I have this in the ConfigureServices Method:

        services.AddIdentityServer()
                .AddApiAuthorization<ApplicationUser, SupportToolContext>();

        services.AddAuthentication()
            .AddIdentityServerJwt();

And this in the Configure Method:

        app.UseIdentityServer();
        app.UseAuthentication();
        app.UseAuthorization();

Which I made according to the asp.net core blazor wasm template with individual auth.

The passwod are correctly filled on Azure itself. What is different on Azure than on my System?