Yeah that’s a pretty funny error, seems to forget that MS office is a very expensive bit of software and doesn’t come included with windows.
It does in recent times. My laptop came pre installed with win 11 and office home 2021(i think).
All i had to do was click activate to link the key to my email account. It showed up as a notification on first login.
Even if not activated it still would open files with that warning.
Including a trial to incentivize users into paying for the software doesn’t make it “built-in”.