This was due to a mixin  used in  crm and sales.  in odoo 18 when using mixins there is  this method that sets the rights to none  for the docs beings uploaded. 

def _get_document_vals_access_rights(self):
    """ Return access rights values to create a `documents.document`

    In the default implementation, we give the minimal permission and rely on the propagation of the folder
    permission but this method can be overridden to set more open rights.

    Authorized fields: access_via_link, access_internal, is_access_via_link_hidden.
    Note: access_ids are handled differently because when set, it prevents inheritance from the parent folder
    (see specific document override).
    """
    return {
        'access_via_link': 'none',
        'access_internal': 'none',
        'is_access_via_link_hidden': True,
    }

by overriding  this method and returning null it takes the rights from the parent  folder.

Hii,

Ensure the Document Folder is Shared Properly

Go to Documents > Configuration > Workspaces :

• Open the folder you want to use
• Check:
  • Allowed Groups → should include Employees or the group of your users
  • Access Rights → should be Editor for those users

Create a Document Rule to Capture Chatter Attachments

Go to: Documents > Configuration > Rules → Create

i hope it is use full