Welcome to the Community, J-F M.
It's great to hear that you're using QuickBooks Desktop Premier 2020. As we're regularly adding new features with each new edition, having the latest version of the program helps make sure you have the newest options for managing your books with QuickBooks.
I can appreciate how having additional details for your customers when sending their invoices would be helpful to make sure they're fully informed. At this time, adding a page of additional detail is not something that's available in the QuickBooks Desktop program. As an accounting software, the program is focused on creating transaction forms to send to your clients and doesn't have the option to create other kinds of forms such as a details page.
If what you're hoping to add is standard information that you might send to any client, you can consider customizing your form templates to add the details you need in a custom field. Learn more here: Use and customize form templates
Otherwise this is a great opportunity for feedback. Many of the features available in the program today started as feedback from users like you and I'm happy to share that submitting your thoughts is easy. Simply click the Help menu in QuickBooks Desktop and choose Send Feedback Online.
Enjoy your day.
