Don't worry, the other Office homepage says that it's actually been renamed to just Microsoft 365, not Microsoft 365 Copilot App:

https://www.microsoft.com/en-us/microsoft-365/microsoft-offi...

I got there by going to office.com and clicking Products > Microsoft Office. Lol. Rofl, even. This has made my day. And we all thought calling their third generation console Xbox One was the worst possible branding decision.