Atlassian Confluence can be operated on three different hosting variants:

While the Server & Data Center deployments are completely hosted and controlled by the customer (for example, behind the firewall), the cloud variant is operated entirely by Atlassian.

Confluence Server and Data Center are basically the same product and differ mainly in the server architecture. This difference is not visible to the user.
On the other hand, Confluence Cloud is very different from the other deployments and should be viewed as a completely different product, even if it has a similar name.

The extensions (apps) in the marketplace must also be viewed in this context. The server version of an app is a completely different product than the cloud app. Manufacturers do their best to ensure that the deployments are as similar as possible. However, this is not always possible because Atlassian has limited the technical possibilities in the cloud. This can mean that a smaller range of functions is available, that functions are implemented differently or may not be included.

Macros

Aura Server

Aura Data Center

Aura Cloud

Background Content

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Button

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Cards

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Content has character limitations

Countdown

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Composition

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Divider

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Embed

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HTML

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Panel

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Progress

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Status

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Tab Group / Tab

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Title

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User Profiles

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Features

Unsplash Integration

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In-app News

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Color Management

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Macro Templates

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Live preview in Aura edit dialogs

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Preview in page edit mode

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Most of the macros are previewed

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Most of the macros are previewed

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Most of the macros are previewed

Insert a macro with a body into another macro with a body (e.g. insert Aura Cards into a Background Content)

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Not all macros can be inserted into the Aura Background Content, Panel & Tabs. A full list can be viewed here in the section 'Compatibiltiy overview'

Due to the EOL of Confluence Server, the migration from server to cloud will become more important as time goes on.
As described above, Aura Server and Aura Cloud and Confluence Server, and Confluence Cloud, are completely different products. We have taken the first steps to enable migration from server to cloud. We are in an experimental phase, and the nested macros can be challenging. These are not compatible with the current functional status of the cloud. Unfortunately, we can’t say when a robust migration will be possible.