After installing .NET 9 previews, you can install workloads by following these instructions. For more information read through the documentation.
Install the .NET MAUI workload:
> dotnet workload install maui
...
Successfully installed workload(s) maui.
Verify installation:
> dotnet workload list
Installed Workload Id Manifest Version Installation Source
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maui 9.0.0-preview.1.9973/9.0.100-preview.1 SDK 9.0.100-preview.1
Installing the maui workload includes android, ios, and maccatalyst workloads which may be installed independently. Run dotnet workload search for a full list of available workload configurations.