Pretty sure Clippy is trademarked. Had the same idea but did not go through with it because of the TM.
Actually this says the trademark is pending them proving they are using it and they aren’t so they keep filing extensions. Also it’s limited in scope to word processing (at there is lots of back and forth with the trademark office about that)
The character is actually named Clippit. Although maybe MS trademarked Clippy after it became the more common name.
Trademarks have to actually be used to remain enforceable, I think. Not sure MS could claim Clippy after all this time, not that they might not try.
Three fact that it's not a product anymore doesn't mean it's unused; a quick search says they at a minimum used it in 2021: https://www.microsoft.com/en-us/microsoft-365/blog/2021/07/0...
Microsoft uses Clippy for the paperclip emoji in the Fluent Emoji set. The trademark is why the open source version of Fluent Emoji doesn't use Clippy's likeness.