Based on the issue #244 LangVersion preview is needed to allow a partial property with a default value. .NET 10 comes with CSharp 14 features enabled and therefore also the field keyword is available by default.
Therefore the check in ReactiveGenerator.Execute could be changed to >= LanguageVersion.CSharp14
For this to work, the Microsoft.CodeAnalysis Packge version override has to be set to Version 5.0.0. I havn't created a PR because I do not know if I am allowed to change the ReactiveUI.SourceGenerators.Roslyn4120.csproj or add an additional ReactiveUI.SourceGenerators.Roslyn5000.csproj.