I am actually really suprised by the strong sentiments Invictus is bringing up.
Invictus is a literary name. People love literary names. From Shakespeare to Lord of the Rings to Game of Thrones, to A Court of Thorns and Roses.
Invictus is an unusual name, but it is still recognizable, and feels powerful. People usually react positively (in naming communties at least) to other names that follow this convention. Odin, and the previously mentioned Odeyseus, for examples.
Invictus has nickname potential. Indy or Vic come to mind. I personally think this enough to give your child options even before considering middlenames (or as I’ll bring up later, surnames).
I knew a kid named Marmaduke that just went by Duke. Once I used his full name. He got shy, giggled, and ask how I knew it. His parents got to name him they way they wanted to, what was meaningful for them, and his peers got to call him something else. When he is older, he can lean into the uniqueness of his full name or stick with his nickname.
Stone is cool. It fits with the nature name trend at the moment and the surname one. I knew a man who went by this (it was his surname).
In my own life, I am strictly called by my last name by certain people. So is my cousin. We have nicknames of our surname(s) on top of our first names and the nicknames people came up with for those first names and our middle names. If we didn’t want to go by our full first names, we have options gallor.
Alexander is a handsome name and I get the idea of using it to “ground”. I myself often do that when playing around with more unconventional names I like. However, I think if you like Invictus Stone, I don’t think you should have to add a second middle just to make it more palitable for the masses. Your kid will have lots to play with and spin, even without it.