A content audit is a site review to see how content is structured and used.
Create content audit views
Create a content audit view, or add displays to the content admin view.
For each content type, create a display showing a table with all the fields.
Configure the displays as tabs on the content page.
Views can't do secondary tabs, try the Views Local Tasks module or create a *.links.task.yml file.
Try the Views Attachment Tabs module to automate the tabs setup.
Filter Format Audit module
Get a report of the HTML in your content.
https://www.drupal.org/project/filter_format_audit
Entity Usage module
How can you tell where a piece of content is displayed in the system?
The Entity Usage module can track where an entity is used in a reference field, and provides a tab with a listing.
This is an area where Drupal core is quite limited.
Content Model Documentation
Provides a few helpful reports.
Entity relationship diagrams with mermaid.js.
