I keep getting popup messages from Avast offering a discount to upgrade to Premium. There is no option to dismiss the popup and all I can do is reboot, which is inconvenient when I am in the middle of doing something.
→ Which version of Avast Free…?
→ OS…? (32/64 Bit…? - which SP/Build…?)
–>Any other anti-viruses installed or have been installed?
Previously I think there was the X in the top right, failing that I feel there should be a No Thanks option.
This certainly needs to be fixed by Avast.
In the meantime, you could try the old school Alt+F4 key together to close the active window. Ensure that this window is the active window before using this key combination.
You could also do the following:
https://screencast-o-matic.com/screenshots/u/Lh/1555868698095-56168.png
Another pitfall that’s not likely to make friends and increase customers. 
+1