51-android.rules             100%[===========================================>]  21.74K  --.-KB/s    in 0.01s   

2020-06-07 16:55:22 (1.49 MB/s) - ‘51-android.rules’ saved [22260/22260]

Installed udev rules and added your account to the adbusers group.
You will need to log off and log back in again or reboot for the group permissions to take effect.

If you are not certain what else to do and it still fails, reboot your computer.

Now installing signify. Beware: the signify package in Debian and its derivatives is very old and may be missing security updates.
Reading package lists... Done
Building dependency tree       
Reading state information... Done
signify-openbsd is already the newest version (23-1).
The following packages were automatically installed and are no longer required:
  fwupd fwupd-signed fwupdate-signed libfwupd2 libido3-0.1-0 libsmbios-c2 libxmlb1
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

You now are ready to download and install GrapheneOS on this operating system.

Follow the instructions on https://grapheneos.org/install#enabling-oem-unlocking
Good luck.
patriot--os@patriotos-System-Product-Name:~/Downloads$