Reproduction steps:
1. Delete all Unity cache folders to make sure the "Unity Editor Update Check" window will appear
2. Create a new project
3. Close the blank "Unity Editor Update Check" window that is opened automatically
-- observe crash

Reproducible with: 2019.4.16f1, 2020.1.10f1, 2020.2.0f1
Could not test with: 2018.4.27f1 ("Unity Editor Update Check" window wouldn't show up), 2021.10a3 (alpha and beta versions are always reported as up to date)

Note:
- Crash was first reproduced with macOS, but later also occurred on Windows. The first line of the stack trace on Windows:
SerializableManagedRefsUtilities::BackupAndDeflateAll

- Console is spammed with NullReferenceExceptions
- Crash is not reproducible when manually opening the "Unity Editor Update Check" window after creating a project
- The first step might not be necessary, but it helped when testing for the "Unity Editor Update Check" window to appear more regularly when creating a project