This has been broken for me, as well, since late Feb 2025. Today, 3/13, it seems to have magically fixed itself. When I clicked the OneDrive icon in the taskbar, clicked Open folder, and clicked the correct shared OneDrive Documents folder in the Quick Access pane, I now have access to my shared OneDrive folders. Everything is a few weeks' behind on syncing, so this is taking a while. But files that have been there since before this fiasco started, are fully accessible by clicking on them in File Explorer. I'm still missing my pinned settings in the File Explorer Quick Access pane that went to my shared OneDrive folders, and I'll try re-adding those shortly.
I'm so relieved, and desperately hoping this continues to work. It's cost me untold amounts of time, energy, and frustration over the past few weeks to have my workflow so deeply disturbed.