Currently, as the default feature in Dynamics 365 (online), there is no way to copy [Opportunities] entity record from [Sales Hub] app.
The workaround that users are aware of is to copy it by using a workflow or copy it from [Project Services] app.
The first workaround requires a long steps to be setup, and the latter is not practical for users who do not use [Project Services] app.

Therefore, it would be much user-friendly if the feature is implemented on Dynamics 365 (online) and they become able to copy [Opportunities] entity record from [Sales Hub] app.