Windows Defender in 2021
Most experts would advise you not to rely on MS Windows built-in antivirus due to its unreliability.However, that is no longer the case since 2019.
Before now, Windows users would usually deactivate Windows Defender and install other third-party antivirus programs. Things have significantly turned around.
In 2020, Microsoft Defender was voted one of the best antivirus applications. AV-Test, an independent testing lab, carried out thorough testing in May-June 2020. Windows Defender got a 6.0/6 score in the AV-Test report, which is quite incredible.
I say NO you do not need 3rd party antivirus apps in windows.
This is now a user preference choice, but it is not needed