The best option for the developer to improve the performance of the component is:

B. Use a selective SOQL query with a custom index.

A selective SOQL query is a query that filters by an indexed field and returns a small number of records compared to the total number of records in the object. A selective query can improve the performance and speed of the query, as it avoids scanning all the records in the table and uses the index to quickly locate the matching records.

A custom index is an index that is created on a custom field by Salesforce support or by marking the field as External ID or Unique. A custom index can make a SOQL query selective if it filters by that field and meets certain conditions, such as using an equality operator, not using a negative operator, and not using a function.

The other options are not suitable for improving the performance of the component for the following reasons:

- Option A is incorrect because using setStorable() in the Apex method will not improve the performance of the component. setStorable() is a function that marks a server-side action as storable, which means that its response is cached on the client side and can be reused for subsequent requests. However, this function only works for Lightning Aura components, not Lightning web components.
- Option C is incorrect because returning all records into a list when the component is created and filtering the array in JavaScript will not improve the performance of the component. This approach will consume more memory and bandwidth, as it will load all the records from the server to the client, regardless of whether they are needed or not. It will also make the filtering logic more complex and error-prone, as it will have to handle different data types and formats.
- Option D is incorrect because using SOSL to query the records on filter change will not improve the performance of the component. SOSL is a language that performs text searches in records across multiple objects....