This is because shared links will now be a part of a newer system that Google believes enhances security. On YouTube, the new links are significantly difficult for people to guess or even access without authorised access. The new links also tie more activity to certain accounts and require users to log in, which enables access to be tracked and it becomes a part of their profile.
On YouTube the changes will impact public videos that have been marked as “Unlisted.” As mentioned in a post, Unlisted videos that have been before 2017 will experience a change of status beginning 23 July. Private videos work now by killing old links and the sharing is only limited to 50 people having a Google account to be able to view it.
All users who want to keep sharing their old Unlisted videos with public links, embeds as well as comments, will have to choose a per-account basis by filling a form next month. Another option that is available to such users is to reupload the videos and let them be marked as Unlisted.
Google Drive is also undergoing some change. When users now click a link to access files over cloud-storage they will need to include a resource key that identifies who is given access. Google/Gmail account and use Drive, then If you have a Gmail account and use Drive, you’ll receive an email after 26 July that will alert you if any files will be impacted due to this change.
In case your account has some links that will get affected then you must opt out of the security update prior to 13 September. Also, if you are using the Google Workspace managed by someone else then it will perhaps be a little difficult as the administrator will be required to opt out or enable individuals to remove it from certain files.