There are various types of black screen on boot (with only mouse visible, with blinking underscore, etc), which can occur for various reasons. This wiki page addresses some of the common causes and basic troubleshooting steps to try.
If you are using Nvidia GPU, be sure to check suggested steps on System will not boot after Nvidia driver update page.
For more general approach, first thing to do is entering TTY terminal:
Ctrl + Alt + F3 on the black screen during boot to enter the TTY terminal. Skip to Step 2 if it succeeds.If key combination fails, reboot into GRUB menu and try to boot an older kernel (button down on kernel list, enter). If this works, check step 5.
If this also doesn't work:
-- on GRUB menu, press 'e' when the list of kernels show, look for the line with:
`quiet splash` , remove both and add the number 3 at the end, then press
`Ctrl + X`

If you somehow forgot your username, use root to enter as superuser with same password (unless you made separate password for root during Nobara installation).
nmcli tool.To check the list of saved connections:
nmcli con show
To enable WiFi connection of selected SSID (name of the link):
nmcli connection up id "Your-SSID-Name" --ask
Verify that you have internet:
ping -c 4 google.com
nobara-sync
Be sure to read updater logs. It's difficult to scroll up on TTY, so to read full logs, use less ~/.local/share/nobara-updater/nobara-sync.log (navigate with arrow keys, PgDn/PgUp, q to close) or create link to share the logs and view them online: cat ~/.local/share/nobara-updater/nobara-sync.log | npaste
Often update errors are caused by the conflicts due to package duplicates.
Read the wiki page Updating error: How do I diagnose and resolve duplicates?
sudo dnf reinstall kernel*
sudo dracut -f --regenerate-all
reboot
If any of these steps produce an error, note it and consult our Discord for further help.