Different user roles in Proposales have different access levels.

Admins can access all content, templates and settings. Users can not access these account settings but they can still send proposals.

If you used to be able to see 'Content Library' but no longer can, this means you have been changed to a User role. You can discuss this with your manager if you need some help with the content. They can decide to change your role if you both agree it would help.