This is a security setting that allows the files you upload/insert in Sheets/Docs/Slides to be accessed by other users who have access to the respective files.
You can share some files with one type of access and others with a different type of access. The access setting must be set before you insert/add files to your Sheets/Docs/Slides. The default setting is PRIVATE.
The options from the most secure to the less secure:
PRIVATE – Only people explicitly granted permission can access the files inserted with FileDrop.
DOMAIN WITH LINK – People in your domain who have the link can access. Not for users with @gmail.com.
DOMAIN – People in your domain (email@domain.com) can access. Not for users with @gmail.com.
ANYONE WITH LINK – Anyone who has the link can access. For any type of Google emails or Workspace accounts.
ANYONE – Anyone can access. For any type of Google emails or Workspace accounts.
If you already added files to your Sheet that are private and you want to share them with someone you need to share the files manually or in bulk.
Share files manually
Go the the files folder >> select the files>>Share
And select the appropiate settings and add the email address of the person you want to share the files with.
Share files in bulk
Please see this feature and steps to share files in bulk with FilDrop.