Explanation
Dynamic actions are a new feature that allow app builders to create custom buttons or actions that can call Lightning Web Components and display them conditionally based on field values or other criteria. Formula fields, AppExchange products, and custom links are not able to call Lightning Web Components.

Explanation
The app builder should do three things to optimize mobile experience:
Use Global Actions to make it easy to perform vital functionality on mobile: Global actions are actions that allow users to create records or perform tasks from anywhere in Salesforce. They are displayed in various places in Salesforce mobile app, such as action bar, action menu, or publisher. By using global actions, the app builder can make it easy for the appraisal team to perform common tasks on mobile, such as creating a new appraisal record or logging a call.
Minimize the amount of formula fields and lookup fields to reduce page load time: Formula fields and lookup fields are types of fields that can affect the performance of Salesforce mobile app. Formula fields are fields that calculate a value based on an expression or formula. Lookup fields are fields that create a relationship between two objects and allow users to select a value from a list of records. Both types of fields can increase the page load time on mobile devices, especially if they are complex or reference many other fields. By minimizing the amount of formula fields and lookup fields, the app builder can optimize the mobile experience for the appraisal team.
Put the most important fields in the compact layout so they are easy to find: Compact layouts are layouts that display a record's key information at a glance. They are used in various places in Salesforce mobile app, such as record highlights, list views, related lists, and lookup dialogs. By putting the most important fields in the compact layout, the app builder can ensure that the appraisal team can easily find the information they need on mobile devices. Option B and D are not things that an app builder should do to optimize mobile experience.

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