Click the AdGuard icon at the Menu Bar - go to Advanced - Reset settings... and quit AdGuard.
In the Spotlight Search, type Terminal - enter
sudo rm -R /Library/Application\ Support/com.adguard.adguard and execute
Restart your computer.
Open the Terminal again, type
ls -al /Library/StagedExtensions/Library/Application\ Support/com.adguard.adguard/ and execute. You should receive the following:
No such file or directory
Start AdGuard, type in login and password when prompted.