No, though it could be the first character in a hashtag. A hashtag includes the characters that follow.
EDIT: The article I linked to says that in Canada, it’s typically called the “number sign”, in the US, the “pound sign”, and in the UK, the “hash mark”.
It depends on the definition of “support ended”. Like, there are various forms of extended support that you can pay for for versions of Windows, and some companies do.
https://en.wikipedia.org/wiki/Windows_XP#Support_lifecycle
So for those, we’re all definitely a decade past the end of normal support. However, they have their extended support packages that can be purchased, and we aren’t a decade past the end of those…but most users probably aren’t actually getting those:
For the typical, individual end user, one probably wants to have been off Windows XP by 2008.