Does windows 10 needs an antivirus or not?

Windows 10 comes with a "default" anti-virus:   Windows Defender.   If you [or your machine's manufacturer] don't install/enable a [paid or free] antivirus of your [/their] choice, then Windows Defender will activate itself to protect you.   However, if you [or your machine's manufacturer] DO decide to install an alternative antivirus program, then Windows Defender will disable itself, deferring virus protection to your chosen program.