Not sure if it helps you but its how we do it, create Debug configuration, then within the csproj file you can do something like:

<PropertyGroup>
<TargetFrameworks>net9.0-android;net9.0-ios</TargetFrameworks>
<Configurations>Debug;Foo1;Foo2;</Configurations>
</PropertyGroup>

<PropertyGroup Condition="'$(Configuration)' == 'Debug'">
	<DefineConstants>DEBUG;FOO1</DefineConstants>
</PropertyGroup>
<PropertyGroup Condition="'$(Configuration)'=='Foo1Debug'">
	<DefineConstants>FOO1;DEBUG;</DefineConstants>
</PropertyGroup>
<PropertyGroup Condition="'$(Configuration)'=='Foo2Debug'">
	<DefineConstants>FOO2;DEBUG;</DefineConstants>
</PropertyGroup>

<Choose>
	<When Condition="$(DefineConstants.Contains('DEBUG'))">
		
	</When>
	<Otherwise>
		
	</Otherwise>
</Choose>

<Choose>
	<When Condition="$(DefineConstants.Contains('FOO1'))">

         </When>
	<Otherwise>
		
	</Otherwise>
</Choose>

When you need hot reload to work switch to Debug Configuration and just make sure the csproj file applies what you need for which ever custom config you opted for.

Furthermore when publishing just provide the -c flag for the specific custom release config like so:

dotnet publish -f net9.0-android --configuration FooRelease

Be careful with custom configurations names. Internally MAUI/.NET set some MSBuild properties depending on the names "Release" and "Debug". If you have a name like DevRelease and expect a Release-Build you will not get a Release-Build.
dotnet/sdk#31918

Exactly as @LeoJHarris says. Create a custom property in csproj and setvalues depending on that.
@davidortinau
Is it possible to add this to the documentation, as it's not 1st or 2nd time people are asking how to make custom configurations?

Be careful with custom configurations names. Internally MAUI/.NET set some MSBuild properties depending on the names "Release" and "Debug". If you have a name like DevRelease and expect a Release-Build you will not get a Release-Build. dotnet/sdk#31918

@AlleSchonWeg We are aware of it but what's the alternative? We have been doing this since the Xamarin days and we have not noticed any issues. That being said if you know the complete list of MSBuild Properties you can manually add them to csproj anyway.

Be careful with custom configurations names. Internally MAUI/.NET set some MSBuild properties depending on the names "Release" and "Debug". If you have a name like DevRelease and expect a Release-Build you will not get a Release-Build. dotnet/sdk#31918

@AlleSchonWeg We are aware of it but what's the alternative? We have been doing this since the Xamarin days and we have not noticed any issues. That being said if you know the complete list of MSBuild Properties you can manually add them to csproj anyway.

There is no perfect alternative. I tested a lot and never had all properties set like the default debug/release configurations. Finally i created a custom MSBuild property MyEnv and set it at the beginning of my csproj and comment/uncomment what i need. By default MyEnv is not set, when i build the project with VS:

<Project Sdk="Microsoft.NET.Sdk">
	<PropertyGroup Condition="'$(Configuration)'=='Debug' And '$(MyEnv)'==''">
		<!--<MyEnv>LocalDebug</MyEnv>-->
	</PropertyGroup>

	<PropertyGroup Condition="'$(Configuration)'=='Release' And '$(MyEnv)'==''">
		<!--<MyEnv>Prod</MyEnv>-->
		<!--<MyEnv>Staging1</MyEnv>-->
		<!--<MyEnv>Staging2</MyEnv>-->
	</PropertyGroup>
	...
</Project>

Then i set values depending on MyEnv:

	<PropertyGroup>
		<DefineConstants Condition="'$(MyEnv)'=='' And '$(Configuration)'=='Release'">$(DefineConstants);PROD;XX;YY</DefineConstants>
		<DefineConstants Condition="'$(MyEnv)'=='' And '$(Configuration)'=='Debug'">$(DefineConstants);LOCAL;XX;ZZ</DefineConstants>
		<DefineConstants Condition="'$(MyEnv)'=='Staging1'">$(DefineConstants);INT1;XX;YY</DefineConstants>
		<DefineConstants Condition="'$(MyEnv)'=='Staging2'">$(DefineConstants);INT2;XX;YY</DefineConstants>
	</PropertyGroup>

You can also set other properties like outputpath depending on MyEnv. When build/publish with cli and you want Staging1 for example you can set MyEnv to Staging1 (dotnet build /p:MyEnv=Staging1). It depends on you what you prefer. Set via csproj or via cli.