For most users, it won’t affect the macros at all. Macro content will be migrated automatically as a part of migrating all other page content. As an administrator, you will need to manually migrate the custom user macros and math block template in the LaTeX Math settings. If you used the default values on Server then no action is necessary.
What differences are there between LaTeX Math Server and LaTeX Math Cloud?
Some Server features are not available on Cloud, please see the following list:
latex macro: On cloud the Math, Unit and Reference macros are supported, but the non-math latex macro is not.
Editor features: The page editor in Cloud will not automatically create LaTeX Math macros when typing or pasting latex syntax such as \[ x \]
Can I Migrate my Confluence Server License to Confluence Cloud?
Unfortunately, no. Server licenses are one-time purchases with optional maintenance, whereas Cloud purchases are recurring subscriptions. As such, existing Server app licenses cannot be transferred or credited to Cloud. These are independent licenses that need to be paid for separately.
If you purchased your Confluence Server license directly via the Atlassian Marketplace, you may contact Atlassian Support to see if you are eligible for a refund.