The email button item will not be visible on the Lightning record page if the page layout includes the case feed component or if the email button contains JavaScript. The case feed component replaces the standard buttons on the page layout with actions in the feed. The email button item will not work if it contains JavaScript because JavaScript buttons are not supported in Lightning Experience.

The "Accordion" Lightning component is designed to break up content into collapsible sections. This component would be suitable for managing the visibility of large numbers of fields by grouping them into separate tabs or sections that can expand and collapse. This makes navigation easier and declutters the interface.
A: Highlights panel is used for displaying key record information at the top of the page and is not designed for managing multiple fields.
B: Record detail displays all fields on a single layout, which does not suit the requirement to break up the fields.
C: Field section does not exist as a standard Lightning component. Reference: Accordion Component in the Lightning Component Library

A text-only Visualforce page can be used to show a text notification on a case record page based on a condition. The Visualforce component can be dragged into the Case Lightning page and its visibility can be set to show when the account support level is platinum. This is the simplest and most flexible way to meet the requirement

The app builder should recommend building a global action to create Contacts. A global action allows users to create records quickly from any page in Salesforce on their mobile devices. The app builder can also specify predefined values for some fields in the global action, such as Account Name or Phone Number, to make data entry easier for users. Option A is incorrect because customizing the mobile menu to move Contacts to the top does not help users create new contacts quickly or follow up later. Option C is incorrect because adding a compact layout to Contacts does not help users create new contacts quickly or follow up later, but rather shows them more fields on record detail pages or list views. Option D is incorrect because using Path and setting pre-defined values does not help users create new contacts quickly or follow up later, but rather guides them through different stages of a record.