Hi @Gus ,
Thank you for posting in this community.
To change the share settings of all content in a SharePoint site at once, you can share a specific sharepoint site directly to registered users, please follow the steps below:
- Go to the site and select “Settings” (gear icon) and then “Site Permissions.”
- "Advanced permissions settings.”
- "Grant permissions"
- Enter the names of the users you want to grant access to and select their level of control (Read, Edit, Full Control).
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.