Black screen with cursor on the top left while upgrading to 20.04

While I am working on my laptop, a popup (notification) came for upgrading my 18.04 system to 20.04.

I accepted it and after an hour the system got logout. I tried a lot to log in, but the same log-in screen is appearing.

So, I did the hardware shut down.

After that, the system is not normal. A black screen is appearing with a blinking mouse on the top.

How to fix it?

My trials:

#1:

I can go to bios menu via F12.

I tried with the two options ubuntu and its next one, but result is same as title.

#2

I can go to terminal type with some random clicking on Atl+ctrl plus some F keys. I tried with these, but of no use.

I can update, upgrade etc., and the lsb_release -a is showing 20.04

Is it possible to fix it from tty?