Unity Safe Mode is available in Unity 2020.2 beta. This improves how Unity behaves when opening a project that has script compilation errors.

If there are compilation errors at Editor startup, you will be prompted to enter Safe Mode. This mode is designed to provide the best environment for resolving compilation errors, so that you can quickly return your project to a functional state, without waiting for all of your project’s assets to be imported. This feature will simplify and speed up the process of upgrading a project to a new Unity version, and it will help teams working on large projects by reducing the number of cases in which the library folder contains incorrect import artifacts.