We currently require Unity version 2019.3.12f1 or later. The plugin can be installed to Unity projects with version 2019.3.12f1 or later.
But for developing the Unity Plugin, please use exact version Unity 2019.3.12f1. If you try to open Unity plugin project with a different version, Unity will want to upgrade/downgrade the project. To not have such a problem, use exact Unity 2019.3.12f1 version for development of the plugin.
Version 2019.3.12f1 is required because we require Swift libraries: https://issuetracker.unity3d.com/issues/ios-swift-language-version-is-not-set-in-xcode-build-settings-when-a-swift-source-plugin-is-added-to-an-unity-project
Version 2018.1 is required because we use NewtonSoft for JSON serialization as the DefaultJsonUtility class cannot serialize arrays, sets, and dictionaries.
We need to use the .NET standard library 2.0 to avoid the error "il2cpp not supported" from NetwonSoft and that requires Unity version 2018.1
Read more on https://docs.microsoft.com/en-us/dotnet/standard/net-standard and https://stackoverflow.com/questions/16359628/json-net-under-unity3d-for-ios;