EDIT: After 1 1/2 days trying to solve the problem, folders are back with Shared status and proper url-links attached... It just happened while writing my comment. However, I was a bit worried when 10Gb of important files were not accessible even if they used to be stored locally.
This problem appeared on my computer recently. Existing desktop folders stopped working. I tried to re-link them in web-onedrive, where shared folders were accessible under shared-tab, but were not visible in My files any more. At first the desktop folders were replaced with url-links, but after some time, renaming and deleting shared folders and undoing this, one out of three folders returned to shared folder whereas two others turned into private folders. The shared folder has url-link in web-onedrive when you open its settings, but two others don't and it is impossible to add link. Trying to re-share folders function does not send email for activating these previously shared folders. The difference with folders turned into private is that they are a lot bigger in size.
Another thing I noticed, sharing folders from personal 365 onedrive to corporate onedrive is not working. Curiously, in the corporate web-onedrive there are functions in settings' main menu not available in personal onedrive, like Restore and Sync. Restore can be found under further settings, but 2FA is not working properly and restore cannot be used (to see if it would help, but I doubt it - I tried re-linking onedrive and resetting it etc. already).
Possibly unrelated, but when using Office apps on desktop, whenever I try to "Save as" a file opened from onedrive, the local file path is changed into https://d.docs.live.net -url when browsing folder, which I find annoying.