The problem has been solved. Here is the documentation for anyone running Linux in Virtualbox on Mac:
For installing the latest version of ADB and Fastboot in Ubuntu check this video tutorial: https://www.youtube.com/watch?v=7ZDinK5zEtM
In the video you can see Kali Linux but the commands are the same as for Ubuntu.
For connecting your device to Virtualbox the right way follow these steps:
- Go to the settings of your Linux virtual machine (in Virtualbox)
- Click on ports
- Add your phone as USB device by clicking the usb + icon.
- Restart your phone in fastboot mode (hold volume up + power).
- Add your USB device again. You will see it has a different name. Add it without deleting the other one.
- Download the latest version of the VirtualBox Oracle VM VirtualBox Extension Pack on your mac and install it.
- Go to the settings of your Linux VM once again and click the ports menu.
- A toggle appears. Switch from USB 1.1 to USB 3.0
Install Easy Installer using the instructions here on the website and you are ready to go!
@Ingo_FP_Angel @aibd Thanks again for your help! I have been using /e/ for half a day and it blows my mind. Awesome OS!