Where do I find my metamask seed phrase on iCloud?

Ask metamask. From their support documentation it sounds like that is never saved in any human readable form since it is a vital security phrase used to recover and access the account.

As with all such vital security passwords or phrases or codes, no backup ever stores them in any human readable format. It is up to you to remember them or keep them somewhere you can recall them.

Regrdless, ask metamask support about their software or app -> https://metamask.zendesk.com/hc/en-us