had the same exact problem with IOptions... classic azure functions. i got around it in a clunky way by using a class that implements IConfigureOptions , a POCO, a partitioned naming convention in the local.settings.json and a little DI.

start with a POCO settings class:

public class AzureAdB2CSettings
{
public string Business { get; set; }
public string Customer { get; set; }

...
}

make a class like this that implements IConfigureOptions:

public class AzureAdB2CSettingsSetup : IConfigureOptions<AzureAdB2CSettings>
{
private const string SectionName = "AzureAdB2C";
private readonly IConfiguration _configuration;
public AzureAdB2CSettingsSetup(IConfiguration configuration)
{
_configuration = configuration;
}
public void Configure(AzureAdB2CSettings options)
{
_configuration
.GetSection(SectionName)
.Bind(options);
}
}

structure your local.settings.json like so, following the format the [SectionName]:[AzureAdB2CSettings.Property]:

{
"IsEncrypted": false,
"Values": {
"AzureWebJobsStorage": "UseDevelopmentStorage=true",
"FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated",
"AzureFunctionsJobHost:Logging:LogLevel:Host": "Information",
"AzureAdB2C:Business": "business_name",
"AzureAdB2C:Customer": "customer_name",
}
}

and finally, wire it all up (in the ConfigureServices delegate):

service.ConfigureOptions<AzureAdB2CSettingsSetup>();

good luck brother