How to reproduce:
1. Open the attached project from the given link in Edit

Expected result: Project opens successfully within an hour
Actual result: Project freezes for 2-10 hours when opening for the first time

Reproducible with: 2019.4.13f1, 2020.1.10f1
Not reproducible with: 2020.2.0b11, 2021.1.0a4

Notes:
- Not reproducible with macOS 11.0 Beta Big Sur (takes about 20 mins to open the project)
- Reproducible with macOS 10.15.7 Catalina
- Not reproducible with ADBv1
- When importing the project for the first time, Unity hangs a random time between two to ten hours. On later versions of the project, the editor stalls for eight to twenty hours
- The editor shows a dialog indicating that the import process has finished (see ImageA.png). And there is a large memory consumption (check the activity monitor). Also, if the process is forced to quit, it prints on the log file the following message: [Unity Package Manager (Upm)] Parent process [47580] was terminated
- On 2020.2.0b11 and 2021.1.0a4 upon opening notifies that changes to read-only file manifest.json are required, prompts entering safe mode, and finally opens the project when clicking to ignore safe mode and import finishes