ClimateControl.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

Program.cs

List<Status> statuses = new()
{
    new(Category.Normal, new(20, false, 20)),
    new(Category.Warning, new(20, false, 60)),
    new(Category.Danger, new(20, true, 60)),
    new(Category.Danger, new(100, false, 20))
};

foreach (Status status in statuses)
{
    string message = status switch
    {
        {Category: Category.Normal} => "Let the good times roll",
        {Category: Category.Warning, Reading.PM25: >50 and <100} => "Check the air filters",
        {Reading.PM25: >200 } => "There must be a fire somewhere. Don't go outside.",
        {Reading.SmokeDetected: true } => "We have a fire!",
        {Category: Category.Danger} => "Something is badly wrong",
        _ => "Unknown status"
    };

    Console.WriteLine(message);
}


record struct Reading(int Temperature, bool SmokeDetected, int PM25);
record struct Status(Category Category, Reading Reading);
enum Category
{
    Normal,
    Warning,
    Danger
}

Excellent! Thank you @algonzalez