There’s a clickable link with is supposed to allow installation but doesn’t work. I’ve disabled the antivirus completely until new advice.
I’ve disabled Hardened Mode completely on Settings → Antivirus.
If you would look at the bottom right of the pop-up you will see “add an exclusion”. 
If you download anything, Avast hardened mode will act up multiple times, so if you have any software do anything to your PC, it will act up and if you press “Add Exclusion” when it installs another item it will pop up again… Just go into Settings>>General>>Hardened Mode and turn off.