Some devices running Ubuntu 18.04 LTS, 20.04 LTS and also Ubuntu based systems have touchpad issues when the system is put into Lock/ Hibernation mode. The mouse pointer becomes unusable.
This problem persists despite running on Kernel 5.4.
A quick, yet temporary fix is to reinstall the mouse drivers.
Now, since your mouse is stuck you can use your keyboard to launch the gnome-terminal using shortcut
Ctrl + t and fire up the commands :
sudo modprobe -r psmouse sudo modprobe psmouse
Ta-da! Now your touchpad is back in action.
This also applies to systems running Debian OS too.