First you have to make sure you configured you application to load the config correctly:
Example from Serilog:

static void Main(string[] args)
{
    var configuration = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json")
        .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", true)
        .Build();

    var logger = new LoggerConfiguration()
        .ReadFrom.Configuration(configuration)
        .CreateLogger();

    logger.Information("Hello, world!");
}

If you did this you have to correctly structure your json like this: https://github.com/serilog/serilog-sinks-rollingfile?tab=readme-ov-file#controlling-event-formatting

{
  "Serilog": {
    "WriteTo": [
      { "Name": "RollingFile", "Args": { "pathFormat": "log-{Date}.txt" } }
    ]
  }
}