The current Photos experience documented for Windows does not list a heart button in the viewer toolbar. Instead, Favorites is available as part of the broader photos experience, and recent Photos updates emphasize actions such as edit, print, share, metadata, filmstrip, and multi-view.
Given the steps already completed—repair, reset, reinstall, and reboot—the most supported conclusion is that this is likely a change in the current Photos app experience rather than a local app corruption issue.
Available options from the documented behavior:
- Check whether the photo can still be marked through the broader photos experience where Favorites is supported.
- If the missing control is specific to the current app build, use Feedback Hub (WIN + F) to report it. Photos app feedback can be filed under Apps > Photos.
- If the older workflow is required, open Photos Legacy:
- Open Photos from the taskbar search.
- Select Settings.
- Under Photos Legacy, select Open Photos Legacy.
Photos Legacy is the version documented with favoriting in the toolbar, along with filmstrip and multi-view. It can run at the same time as the new Photos app.