As @aronowski has told you “I pressed Ctrl+Alt+F9 on my keyboard and my
screen went black” is absolutely normal behaviour, although why you
went through that list of commands is not explained.
Your computer is running different consoles - the GUI is on tty1.
When you are in the desktop, you can switch to another tty by pressing
“Ctrl+Alt+FNUMKEY”
You pressed Ctrl+Alt+F9 - that takes you to tty9.
There is nothing listening on tty9 so you got a blank screen.
If you had pressed Ctrl+Alt+F2 you would have seen tty2 where there is a
console login.
When you are already on a console tty you can switch to another by
pressing Alt+FNUMKEY
The GUI is listening on F1 so you can get back to it from a console tty
by pressing Alt+F1
Ctrl+Alt+Del is a standard combo to trigger reboot in systemd
SO this is all standard behaviour.
Since you aren’t able to say what these mysterious messages were, there’s
little more to be said.
What should you do next? Learn not to arbitrarily mash away on the
keyboard.