Oh boy. There are so many factual inaccuracies in that article I don’t even know where to start.
So, the logical course is to begin with the first paragraph:
These all have numerous security advantages, including proper verified boot…
…except if you aren’t using Bitlocker, in which case all an attacker needs to do to gain access to your computer is mount your disks from a Windows installation USB, replace one of the accessibility executables with cmd.exe, reboot, and use the accessibility menu in the lock screen to launch an administrator terminal with full NT/AUTHORITY permissions.
Seriously, the desktop model as a concept is flawed, but Windows takes those flaws to a whole new level. There are many other ways to start an administrator terminal that don’t even involve altering system files, such as getting access to the emergency command prompt by causing a boot failure by changing a few BIOS settings to prevent a complete boot.
… a strict IOMMU…
So does any modern OS? Not sure why this is considered a proprietary advantage.
If you can, stay away from desktop and stick to mobile devices.
We will get to… whatever this is later.
Use Windows 11 (preferably in S mode…
Uhh, don’t. Seriously, just do not. S mode is deprecated and was never truly intended for security. It was simply a way for Microsoft to keep people locked into the Microsoft Store ecosystem so the trillion-dollar corporation can extract more money from you.
If you absolutely do need to use Windows...
…you should definitely NOT use Windows 11 Home or Pro, since telemetry can only be disabled on Enterprise editions. Windows 10 IoT Enterprise LTSC is probably the best version of Windows for our security-focused use cases, but the caveat is that it cannot be legally acquired in the US, so tough luck to Americans I guess.
…whereas macOS has full verified boot to eliminate malware persistence.
Weird idea of what persistence means. Malware can definitely persist in macOS (as it is not a fully stateless OS), though it is indeed harder to access the firmware due to the T2 chip in Macs.
Some of these operating systems do have some privacy invasive telemetry, but it can usually be disabled in the settings
By “some” you mean “all except Linux”, and by “can usually be disabled in the settings” you mean “cannot, without heavy tinkering and breakage of your system, be disabled”. 
The fact that this article believes in such things should be all the evidence you need to stop reading and disregard most of what they’ve said.
Do not use Linux…
I’m not even going to begin with that. Let’s just say it’s pretty easy to see why you shouldn’t use that as a valid source of information. Hint: flatkill.org is listed as an important source, even though it’s followed by a nonsensical description of what Flatpak isn’t.
And now, for mobile. Full disclaimer: I do not use a smartphone, and I am very biased against those tiny surveillance devices we are expected to carry in our pockets. With that in mind…
Mobile operating systems were designed with security as a foundational component… As such, they are far more locked down than other platforms and significantly more resistant to attacks.
“Resistant” is being used very liberally here. Both iOS and Android were subject to various vulnerabilities over the years, including a very recent noclick attack on iOS that made use of unused firmware code that allowed a program to access restricted kernel memory regions.
Now, you can either accept this as a clever exploit that found a vulnerability that Apple forgot about, or you can put on a tinfoil hat and believe that the unused code was a backdoor for some three-letter government agency. In truth, we’ll never know which one is the case.
…which brings us to the main argument against phones:
Use either the stock operating system or preferably, GrapheneOS on a Pixel ≥ 4.
Alternatively, use an up-to-date iPhone, which is comparable to GrapheneOS on a Pixel, and do not jailbreak your device.
Phones are a black box in terms of transparency, and vulnerabilities are bound to happen in black boxes developed in secret engineering labs with no input from the public. The stock OS for Pixels includes many, many proprietary components which the end user has no idea of their function or purpose. The same occurs with iOS, but this time, you don’t even get the FOSS parts of AOSP/Linux.
There is absolutely no way to know how these devices sneak telemetry data off your network, and even if they were magically 100% effective at protecting user data from external threats, there would still be nothing stopping Apple or Google from just uploading your sensitive data to their servers.
Quick note on GrapheneOS:
You’ll end up needing to trust them instead of Google if you decide to install their OS on your Android device. The issue is that they recently had a lot of governance and community management issues that reduced the trust of the community in the lead developer. I’d recommend thoroughly researching the available information on GrapheneOS (and reviewing its source code), and determining for yourself if they’re trustworthy enough.
Stick with the machines you can trust. Never use proprietary code if possible.
Browsers
For security, use Chromium. Avoid Firefox or browsers based on it, as they are currently very lacking in security.
That… is fair. Firefox’s sandboxing has never been as good as Chromium’s. Though I’d still use a Chromium fork with questionable code removed such as ungoogled-chromium instead of vanilla Chromium.
Microsoft Edge is a better choice for Windows users…
No.
Again, there’s a reason why Qubes distrusts itself. Microsoft Edge may have extra features that make use of Windows Defender and other Windows-only tools, but again, you cannot trust Microsoft. There’s no point in being defended from external attackers if the real adversary was already there all along.
For privacy, use the Tor Browser, and consider using the security slider. Do not assume that “hardening” Firefox or other browsers will make it private; it won’t.
Kinda. Indeed, the Tor Browser is what you should use if you need a private Tor connection, but I’d make the case that you can harden your browser against fingerprinting. For instance, the Mullvad Browser is open source and based on the Tor Browser, but it connects either through a VPN or directly to the clearnet instead. It succeeds in spoofing its fingerprint, and CreepJS and EFF’s Cover Your Tracks (formerly Panopticlick) both report a non-unique identifier from Mullvad Browser instances.
For a mixture of security and privacy, use [android browsers] or Brave, although none of these are as good as the Tor Browser when it comes to privacy.
Maybe that’s because Brave accidentally sent Tor requests through the clearnet. Who would have thunk that a company would be more concerned with putting a crypto money-making scheme in the browser than actually focusing on privacy.
Messenger
Use Signal, preferably with a burner or VoIP number.
So, the private messenger asks for your phone number as required data for an account? Use something actually decentralised like the Briar Project, and maybe Matrix in the future once its current encryption issues are fixed.
Lots of hyperbole and outright fabrications here. Please do not take any of the advice on that website into consideration.
So I have to disagree too. I think newbies will do just fine in Qubes. The GUI had most personalized things straight forward on the basic level, I didn’t see the resizing of the Terminal though that I missed until a Qubes Forum poster told me where to click in the GUI.