SIdebar disappear ubuntu 21.04 after CTRL + ALT + F5

I was writing some code in vscode, then I want to compile inside it, but I pressed the key combination wrong, CTRL + ALT + F5. A black screen appeared and ask me to login in a new session. I didn't know how to return to vscode and I reboot my pc. After that, my sidebar disappeared. I tried to change the position from screen from settings, but doesn't worked for me. Can someone help me? PS: I reinstalled also unity, but doesn't worked for me..

Ctrl+Alt+F5 in Linux takes you out of the graphical environment into a text console, tty5. Indeed, you can log in there, and you will end on a terminal prompt. To return to your graphical desktop, hit Alt+F2. Your graphical desktop is running on tty2, the GDM login screen runs on tty1.

You did not tell how you did reboot the PC. "Hard" rebooting by pulling out the power can damage your system, in particular the file system. Always try to reboot a linux system correctly, i.e., if you are on a terminal prompt, with the command reboot, or sudo reboot if you have no permissions to reboot as a user.

For now, your system starts and you can log in. The damage therefore may be minimal. The side bar actually is a Gnome Shell extension called Ubuntu Dock. First check the current settings of that dock in the Settings. It may be set to hide. Second install a tool gnome-shell-extension-prefs. In that tool, you can activate and inactivate extensions. Make sure the extension is enabled. Third, you can try the following command, which will restore all settings of the Dock to their factory default:

dconf reset -f /org/gnome/shell/extensions/dash-to-dock/

You did not explain why you installed Unity. Unity is a different desktop environment. It is the one used on older Ubuntu systems. Currently, Ubuntu uses the Gnome Desktop environment. Installing Unity will not solve issues with the Gnome Shell desktop.

Think twice before manipulating your sytem: only undertake actions after you have understood what they will do.