I moved away from Webroot last summer so I don't have direct experience with Webroot in Catalina and I'm a bit rusty with the script, but here goes. . .

The script I used was very similar to yours except for 2 main differences. The biggest difference was that I didn't have a proxy to deal with. The other difference was in your #copy app from dmg to applications step you're using sudo cp -R --- where I just used ditto to move the app from the disk image to the Applications folder.

I'm not sure either are your issue, but it's also not clear to me where the script is falling down for you. You say "fails once the installer is opened" but that doesn't make any sense to me because at its core, the script curls the DMG and puts it to tmp, mounts the DMG, drags/copies the app to /Applications, sets the client keycode, unmounts the DMG, then cleans up the DMG. So I'm a bit confused because there's really no "installer" involved.

That said, here are the things I'd look at. . .
- First, can you run the script successfully on its own outside of Jamf?
- If you run the script and have a finder window open showing /tmp does it actually download the dmg correctly?
- From what I remember, when the script ran you could actually see the WSA disk image mounted on the desktop as the mount part of the script happens and then disappear as the unmount part happens. Perhaps that's because I didn't use the -nobrowse modifier in my script. Maybe take the -nobrowse modifier out just to see if it's actually mounting the disk image.
- What happens if you take out the lines dealing with the proxy and test on a machine not dealing with a proxy?
- Does Webroot SecureAnywhere.app ever make it to /Applications ?

Sorry to grave dig this thread, but I have a tested working version of that script. Works with Catalina and before. - enjoy

KEY=1111-1111-1111-1111-1111

sleep 2


OS_Version=`sw_vers -productVersion`
echo OS_Version is $OS_Version

clear

if [[ (${OS_Version} > 10.15) ]];

then
   cd /tmp; curl -O https://mac.webrootmultiplatform.com/production/wsa-mac/10.15/latest/WSAMACSME.dmg
    echo "Please wait while file is downloaded and mounted"
    wait 15


    echo "beginning DMG mount"
    hdiutil attach -nobrowse /tmp/wsamacsme.dmg
    echo "Mounted DMG"


    sudo rm -f /Library/PrivilegedHelperTools/com.webroot.InstallerHelperTool

    sudo /Volumes/Webroot SecureAnywhere/Webroot SecureAnywhere.app/Contents/MacOS/Installer -keycode=$KEY install -language=en -silent

    wait 10

    echo "Unmounting DMG"
    diskutil list | grep Webroot SecureAnywhere | diskutil unmount /Volumes/Webroot SecureAnywhere
    echo "Unmounting DMG complete"

    wait 30

    echo "removing downloading DMG from tmp"
    rm -rf /tmp/wsamacsme.dmg
    echo "DMG deletion complete"

    echo "Script complete on Catalina"

else
   echo "Operating System is NOT Catalina, downloading 9.0"
   cd /tmp; curl -O http://anywhere.webrootcloudav.com/zerol/wsamacsme.dmg

   echo "Please wait while file is downloaded and mounted"
    wait 15


    echo "beginning DMG mount"
    hdiutil attach -nobrowse /tmp/wsamacsme.dmg
    echo "Mounted DMG"


    echo "Beginning application copy"
    sudo cp -R /Volumes/Webroot SecureAnywhere/Webroot SecureAnywhere.app /Applications/
    wait 10
    echo "Copy and wait complete"


    echo "Begnning application installation" 

    sudo "/Applications/Webroot SecureAnywhere.app/Contents/MacOS/Webroot SecureAnywhere" install -keycode=$KEY -language=en -silent


    echo "app Installation complete"


    echo "unmounting DMG"
    diskutil list | grep Webroot SecureAnywhere | diskutil unmount /Volumes/Webroot SecureAnywhere
    echo "Unmounting DMG complete"

    wait 30
    echo "removing downloading DMG from tmp"
    rm -rf /tmp/wsamacsme.dmg
    echo "DMG deletion complete"

    echo "Script complete on <Catalina"
fi


echo "Script complete overall"

Anyone else running into issues with Mac OS 11 & 12?