VPN.... should I be using one, or with Windows 11, it isn't needed?

Just finished reading the book called the fifth domain, it's about cybersecurity and cyberthreats.... makes me wonder about one of the things the author's mentioned, using a VPN at all times. The book mentioned the security holes in Windows 10, and wonder since I have upgraded to Windows 11, if I should consider having a VPN?

Best protection against threats is the thing between your ears.

That is very true. I have mainly been a mac user since like 2004 until now and have never used any security suite and have never had any issues with malware.

My wife only turns on the VPN when doing monthly bills and banking tasks.

A VPN can not prevent you, the user, downloading malware, clicking a nefarious email link, filling in a spoof form, starting a cracked game and triggering the hidden payload etc. A VPN is mainly of use to hide your true location, where your access originates from, which has many uses.
Sensible browsing practices and self education along with a reputable anti virus/ malware app (Windows Defender in it's current incarnation is good enough for most people) and maybe a second on demand scanner app (Malwarebytes for example) are the best security features to use.
There are a lot of claims made for VPNs that although not lies are actually also implemented by the OS, your browser/ mail app and your anti virus, it just sounds like they do 'something' to make them more appealing. And not all VPNs are made equal or provide the same service promises.