There's a new model of Raspberry Pi 4 with 8GB RAM, the article should be updated.
For most adults, even the highest-end Raspberry Pi, the Raspberry Pi 4 B (4GB), isn’t powerful enough to serve as a primary PC.
I disagree with that sentence from the article. I use Raspberry Pi 4 with 4GB of RAM as a PC (although overclocked to 2GHz) and it's usable for daily use as a main computer. It all depends on what you expect from it.
It's absolutely quiet, browsing the internet with Chromium or Firefox is good, you can have lots of tabs open (thanks to 4 or 8GB of RAM), video playback is good, has 4k output etc. One advice for novice users - you can actually increase Firefox rendering speed by disabling smooth scrolling. This feature on slower computers adds latency when scrolling - if you turn it off, the latency is shorter.
So, if your daily work consists of reading emails, browsing the internet, even watching some online videos, downloading - then Raspberry Pi 4 with 4 or 8GB of RAM can replace your PC. It doesn't cost a lot in terms of electricity consumption, so it can be left powered on, perhaps finishing long downloads while acting as a file server.
I've even cut a 10 minute CooliPi LN2 submersion video at 1080p/60 using OpenShot, it was a pain until I figured that it got short on memory on a 32bit OS - so I used 64bit Ubuntu with 5GB of swap and then the final export succeeded, allocating some 8GB of ram for the process. Be warned that the new, experimental 64bit Raspberry Pi OS has a 64bit kernel, but 32bit applications, until they recompile it all to 64bit. The new 8GB version should be much better memory wise.
My verdict - it can be used as a PC for daily work and children may use it for remote education in these troubled coronavirus times as a PC (if they don't have enough resources to get a PC to every child in a family) - hook a Raspberry Pi to a TV and voila - another child can have it's own PC for doing homework.