Comment by applfanboysbgon

Without looking at the codebase, I can already say this is a big ask because it uses the Avalonia framework for cross-platform deployment. .NET Framework 3.5 is Windows-only, and there was a heap of massive breaking changes when the .NET Framework was replaced by the superior .NET Core (now just .NET), so it would be a pretty big maintenance burden to try to maintain a separate build target for that.