I'd guess that the absolutely most secure system would be Gentoo, because you compile the binaries yourself and can be absolutely certain nothing suspicious has been added in like what happened with xz. But that requires reading all to the code line by line.
The xz backdoor was added to the source tarball release by an authorized committer. Unless you were building specifically from git instead of from source tarballs, it did not matter whether you compiled it yourself.
It did, however, happen to matter whether you were using a distro that patched openssh to use systemd.
Now, my point is that the average Windows user doesn't even consider that something as simple as disabling the weather widget is possible on Windows. But the moment they go the Linux route, suddenly they go all-in on the ricing? Something isn't right here and that's what I find weird. As if people use their operating systems emotionally rather than practically. What I mean by this, the emotional attachment to Windows is that of hate. This hate then causes people to refuse to try and figure out why something is the way it is, but instead they rage at it and get annoyed by it endlessly. The emotional attachment to Linux is that of openness and freedom, and that leads to people going off the deep end with ricing. Except what the end goal those people had is achievable on both through more or less the same routes, but due to this emotional attachment they were under this false belief that they had to make the switch just to have a nice time using their computer.
I certainly couldn't claim that having to deal with windows never inspires any sort of emotional reaction.
A Windows user seeking control over their computer is like a subject of the UK seeking free speech. Sure, some may exist for awhile - heck, they may even score some activist "wins" by their standards - but as soon as they look elsewhere it becomes rather apparent that they've been looking in the wrong place, and it is far, far easier to simply go somewhere that shares your values.
On Linux, when you consider making some change, it is never a question of "can I do this" - the source is all available, there 100% exists a way to do what you want solely by editing it. Nobody has legal standing to sue you for understanding what your system does and modifying it.
I will freely state that I have never tried significantly customizing windows. For all I know, it is entirely possible to modify some things, within the scope of their initial design, by modifying some settings. Even if you don't need to modify a program, without its source code, you'll probably still need to do some amount of reverse engineering to get complete documentation (there is always an undocumented interaction - if there weren't, the documentation would be semantically equivalent to the source code). Maybe this can get you in legal trouble, maybe it can't. Maybe, like speech in the UK, it will get some people in legal trouble but not others.
Ultimately, your control over your computer only extends as far as the lowest level that you control the software at. Some people at AMD control the lowest levels of software on my computer. It's unfortunate, but it's a temporary compromise, and the scope of people able to interfere with my control over the upper levels is quite limited. Additionally, AMD has neither any justification nor any way to get away with breaking compatibility: the hardware does not change. The probability that I will try accomplishing something on my computer only to eventually hit a brick wall because AMD says "no" or changes something capriciously is basically zero.
And then there's you, advocating "run open source on Windows". Granting every jeet in Redmond control over your computer. Every change you want to make below the surface level is going to hit a resounding "no, and if you so much as mention this again I will bankrupt you in legal fees". They will break compatibility and you will be happy. They will push the forced updates and you will be happy.
You are an architect building on sand and wondering why everyone else you see building is doing so on stone. Perhaps they just have an emotional attachment to stone. It's just as achievable to put a structure on sand, after all.
Enjoy high tides, stalker child!