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There are three audit features salesforce provides us:

1. Field history tracking
2. Setup Audit trail
3. Login History

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There is only one way to do this. We can define apex action in process builder and there must be invocable method available in apex class.

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Dynamic dashboards are dynamic that means they depends upon the current user of the dashboard or the user who is logged in. A dashboard is made dynamic by changing the “running user” from a specified user to “current logged in user”. This setting is in the properties for the dashboard.

As per the scheduling, No, we can't schedule a dynamic dashboard as it totally depends upon the logged in user and shows the data as per the permissions given to that logged in user.

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You can make opportunity's OWD to read write for internal users and by enabling default external access you can set opportunity's OWD to private for external users.

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There are basically three main categories in Salesforce lightning setup:

1. Administration
2. Platform Tools
3. Settings

In settings, we have below options:

1. Company Settings
2. Data Classification
3. Identity
4. Security
5. Optimiser