You're welcome.
This is certainly the first time I have seen this reported in the forums, so I'm at a loss as to what to select.
Clutching at straws a bit here, but give this a try, if you can even get at it. Right click on the avast tray icon and select About avast, From that screen select Troubleshooting and uncheck the Enable hardware-assisted virtualization option and 'left click' the OK button.
Edit: If your mouse is configurable I wonder if switching the Left key assignment to another key would make any difference, but I feel it would just be transferred there.
Edit 2: https://www.online-tech-tips.com/cool-websites/control-mouse-with-keyboard/
Thank you for continuing to try to help.
Tried what you suggested - unfortunately although I could open the About Avast window, I could not click or open Troubleshooting.
With the mouse pointer over Troubleshooting - the Enter key will not open it.
Trying my alternate method of Right-click then the Enter key, merely closes the entire window.
I'm at bit of a loss too, since I've never seen this before either.
Losing the ability to mouse left-click - is such a fundamental thing -
so although I "trust" Avast Free is still protecting - I am very concerned I cannot do any settings
and every time I activate any Avast window (that includes any Avast popups) I lose the mouse left-click.
I have set silent mode to prevent popups -
but when I do any on demand scanning of a file - I cannot see if there is a problem or not....
As a last resort I may try uninstalling and re-installing Avast Free to see if that clears the problem.
Thanks for your help and suggestions.