The clues were right in front of us.
I actually always thought that the mid-aughts trend of putting “My” in front of everything to make it feel personalized was really bizarre, considering that you weren’t ever the person labeling it that. Some developer or marketer you never met named it that. It always annoyed me when my icons started getting relabeled with names that a boomer grandpa might put on them, felt really pandery. Prior to the “My” trend, “My Computer” was just “Computer”.

Didn’t “My Computer” exist since like Windows 95 or so?

Also back when it was first introduced I heard some explanation that people were expected to rename it using their actual name. So something like “Joe’s Computer.” Though I don’t think anyone really did that in practice, which just resulted in everyone always having the “My Computer” icon on their windows desktop and it became the norm.

Yes, Win95 called it My Computer, but at the time it was maybe the only GUI to do that. I remember the trend really kicked off in the early aughts with MySimon and their advertising campaign. Then all of a sudden every header in the OS got the word “My” tacked on.
What do you mean header in the OS? Like .h files? I haven’t seen this.
No like textual headers of windows and settings sections. Shit like “My Settings”.