If you cannot use async and await, use AsyncMethodCaller to easily make asynchronous calls. The code becomes testable and it works perfectly in ViewModels.
See the version list below for details.
Install-Package AsyncMethodCaller -Version 1.0.0
dotnet add package AsyncMethodCaller --version 1.0.0
<PackageReference Include="AsyncMethodCaller" Version="1.0.0" />
paket add AsyncMethodCaller --version 1.0.0
This package has no dependencies.
This package is not used by any popular GitHub repositories.