This might be a case where investigating deeper is confusing you more than it's helping. That actually happens to me a lot!
Sorry, there is ONE plugin, regardless of operating system?
Yes, that's how Inkscape extensions work. You could install the extension if you want to, using the instructions I gave you originally (
https://inkscape.org/learn/faq/#how-install-new-extensions-palettes-document-templates-symbol-sets-icon-sets-etc, or if you need simpler instructions, try the Home tab on this website, down towards the bottom).
But it doesn't sound like it will work after you install it, because as we see for Linux, other things need to be installed. They would probably need to be installed for a Mac too -- not necessarily the same things that you see in the Linux section, but something similar for Macs, maybe. I don't really know exactly what would need to be installed. But as far as I can tell, other things would need to be installed. It sounds like the author hasn't worked that out yet.
Most Inkscape extensions don't need anything more than the extension file that you download. This one, and a few others do need extra things.
However NOT a single one that follows this Path:
/usr/share/inkscape/extensions
NOR a single one that follows this Path:
.config/inkscape/extensions
Is that what you see in Inkscape Preferences > System > User Extensions ? You've got to completely ignore the Linux section for that extension. It doesn't apply to you on a Mac. If this author, or someone else ever makes it to work on a Mac, they will tell you the proper place to install everything. It won't be the same place on a Mac that it is on a Linux.
I'm sure some parts of that extension could be 8 or 10 years old. The original creator of that extension started it at least that long ago. They had a working extension for a few years, and then withdrew it, because they wanted to update and improve it. I never used it, so I don't know how well or not well it might have worked at that time.
Unfortunately, they stalled out on their new and improved version. And eventually someone else picked it up, and made it what it is now. I think that was just a few months ago. So what it is now, as a whole, is fairly current. Although parts might be quite old, I don't really know. So it depends on when those comments that you saw were made, whether they apply to this iteration of this extension, or the first one.
As for hidden files, I had the Windows hidden files unhidden within the first few weeks of using my first computer. And I've never had a problem. Software developers use those files to hold things that users need access to (just like Inkscape does). I can only imagine the internal fights which system developers must have about that.
However, you can always re-hide the files after you install the extension. I mean, you can re-hide them in Windows. I don't know about Macs.