For those of you who have Studio access this can be accomplished by using an Automation Rule. (This uses python code, so if you are on SH they may charge you by the lines of code). 

For our purposes we want to have a customer knowledge base that is accessible to any user given portal access. (Currently we grant portal access)

The goal would be to automatically grant access to the knowledge base when portal access is granted.

To do this we create a single Workspace called "Customer Knowledge Base" then create a child structure below that. 

Once you have your initial workspace built, you will need the ID of this top level article. In Odoo 18 anyway you can see this ID just in the URL

Then create an automation rule on the User model that triggers "On save" when updating "Login" 

You could narrow this down more, but we are actually ok with this being applied to our internal users as well. 

Under action use "Execute Code" and use the following code.

partner_to_invite = record.partner_id

wiz_data = {
    'article_id': 69,
    'partner_ids': [(6, 0, [partner_to_invite.id])],
    'permission': 'read',
    'message': 'added via automation',
}

wiz = env['knowledge.invite'].create(wiz_data)
wiz.action_invite_members()

This is hard coded to the article ID which is our top level workspace as seen in the URL.

When a new contact is granted portal access, a new user is created and automatically added as read to the "Customer Knowledge Base" workspace. This in turn grants them access to all child articles as well as through the search functionality in the portal.

As additional articles are added the users will automatically inherit access.