Fix 1 – Properly remove another antivirus if installed on your pc

If you can’t install an Avira antivirus on Windows 10, it’s because Windows 10 prohibits installing any additional security software.

You should delete the previous antivirus program before attempting to install the new one since two antivirus programs do not work well together. To remove the other antivirus, follow these instructions:

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Turn off Real-time protection by selecting Virus & threat protection settings after clicking the Windows icon, entering the control panel into the search box, selecting Windows security, and then clicking Open Windows Defender Security Center.

After completing the procedures mentioned earlier, Windows Defender is disabled. See whether you can install an antivirus for Windows 10 by trying.

Fix 2: Verify that the Avira free antivirus software you wish to install is appropriate for Windows 10 before you proceed.

The newest operating system is Windows 10. Thus, many antivirus products are incompatible with it. Make sure your antivirus software is appropriate for Windows 10 before using it. See the compatible section on the official website of your antivirus program.

Source - How to fix Blocked Installation error while installing antivirus