The error makes sense, i would not risk that kind of setup… Why you upgraded your Studio and not Orchestrator? That can be treaky to not make mistakes of using upgraded packages your server wont support, maybe you can try manually editing your project settings to indicate version 2018.4.4.
After you’ve ensured that the Studio and Orchestrator versions match, log every dependency used in your project and backup your project.json file. Then open Main in Studio with the project.json file renamed or moved elsewhere. This will recompile your project under 2019.
Next, download all of your project dependencies manually and ensure that the Main.xaml file has the same arguments indicated in your backed up project.json file.