Avira free antivirus for Mac, User Password does not work to finalise install

Hello, after having updated to Big Sur, I experienced several issues that made ma call Appe care and lead to a total reinstall of the original settings of my MacBook Pro, thereby erasing all previous ones. I then tried to reload some of the apps that I used before, Avira free antivirus being one of them. I downloaded the app successfully, but when I reached the install phase, the Mac system asked me to type in my user password in order to allow changes made by the app. I typed said password several times to no avail. This password (that is not a "blank" one) works perfectly otherwise, when I log into my Mac for instance.

How can I successfully complete the install for Avira free antivirus for Mac please?

Thank you so much for your help.