Explanation
An external ID is a custom field that has the external ID attribute enabled, which means it can be used as an identifier when importing and updating records from an external system. It allows administrators to match records based on a unique ID value from another system instead of using Salesforce record IDs, which may not be available or consistent across systems. An auto-number field is a custom field that automatically assigns a unique numeric value to each record, but it cannot be used as an identifier when importing and updating records from an external system because it is generated by Salesforce and may not match with the external system's IDs. A rich text field is a custom field that allows users to enter formatted text, images, and links, but it cannot be used as an identifier when importing and updating records from an external system because it is not unique or consistent across systems. A record ID is an internal ID assigned by Salesforce to each record, but it cannot be used as an identifier when importing and updating records from an external system because it may not be available or consistent across systems. References:
https://help.salesforce.com/s/articleView?id=sf.custom_field_attributes.htm&type=5

Explanation
To require users to choose a specific search engine from a picklist when lead source is "Search Engine", and hide it otherwise, the administrator should create a picklist for specific search engine on the same screen as lead source, and set conditional visibility so that it is only shown when lead source is "Search Engine". This will make sure that users see only relevant fields based on their input. A decision element will create an extra screen that may disrupt user experience. An assignment element will not affect field visibility. A validation rule will not hide fields but only show errors when values are invalid. References:
https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_screen_components_picklist.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements_screen_components_conditional_visibility.ht

Explanation
A flow can be active or inactive depending on whether you want it to run or not. An inactive flow cannot be run by users or processes until you activate it. If a flow in production is supposed to create new records but it is not doing so, it could be because the flow is inactive and needs to be activated. References:
https://help.salesforce.com/s/articleView?id=sf.flow_distribute_activate.htm&type=5

Explanation
Lightning record page is a type of page that should be created to meet this requirement. Lightning record page allows an administrator to customize the layout and components for a specific object record page in Lightning Experience or the Salesforce mobile app. To create tabs for account details, related lists, and chatter feeds, use the Tabs component in the Lightning App Builder and drag the desired components to each tab. References:
https://help.salesforce.com/s/articleView?id=sf.app_builder_record_page.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.app_builder_tabs.htm&type=5

Explanation
Process builder can be used to create a record-triggered flow that executes when an opportunity is closed as won and creates a follow-up task for the owner. Field update can be used to update a date field on the opportunity that can be referenced by a time-dependent workflow rule to create another task after 60 days.
References: https://help.salesforce.com/s/articleView?id=sf.process_which_tool.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.workflow_time_action_considerations.htm&type=5