Until a month or two ago, when you'd go to https://office.com , there was a "Pinned" heading in the panel/section below the filmstrip in "Recommended". When you go there now, the headings are "All", "My recent", "Shared" and "Favorites". It seems like maybe "Favorites" replaced "Pinned", but there are two problems with this:
None of the files I had Pinned in the past were transferred to Favorites. If Feature B is replacing Feature A as a means of identifying important files, than any files flagged by Feature A should transition to Feature B.
The "Pinned" term is still used in the Office desktop apps. For two years, I've been training folks to "Pin" their important files to make it easier to get to them from either the Office portal or the app that created them. As I saw it, this feature was a valuable way to manage the inevitable sprawl that came with Microsoft 365. Users end up with files stored in OneDrive, SharePoint, dozens of different Teams, etc. and Pinning was a way to get back to them easily. You might not remember where you saved that PowerPoint you were working on, but you knew it was a PowerPoint. So, once you pin it, you can easily get back to it via the Pinned section in PowerPoint's backstage.
So, is "Pinning" documents a concept that's gone from the Office portal and Office web apps? Will it also disappear from the desktop apps at some point? And if so, will it be replaced by "Favorites" (which actually match up to the Favorites you set in the portal)? These kinds of unexplained disappearances or changes are a HUGE issue when it comes to user adoption and trust. I get that M365 is "constantly evolving", but there's a responsible way to communicate and manage that evolution that doesn't include pulling the rug out from under users.