Apple and windows are trademarks for software. You would be unable to get the trademark "Apple" for a company selling fruit, or "windows" for a window fitter, and neither could Apple or Microsoft.

𝕏 is a pre-existing symbol used by, and part of a standard character set for, software. You could probably get a trademark on it for a company selling apples, but I highly doubt you could for a software company.

> 𝕏 is a pre-existing symbol used by

"used by" is pretty debatable. Its a fairly obscure character. I don't think being in unicode by itself is sufficient enough to count.

There is also https://www.x.org/ which seems quite slow. I wonder if it's receiving more traffic than usually..