Merg 2 iClouds

What is iCloud account and how it is set up , create an Apple ID with a mail address and sign in with device Use your Apple ID with iCloud - Apple Support

Everyone should have their own Apple ID. Having your own account ensures that your data remains private. Only you can access your information, make changes or delete your content.

, the iCloud features like notes , mails , photos ...are to be turned as on Set up iCloud features on Mac - Apple Support

Sign in to iCloud on all your devices - Apple Support

If there are different devices the Apple ID and its password should be differently signed in , to sync iCloud accounts and iCloud data obviously they should be signed in with same credentials .

So according to the question merging two iCloud accounts with different Apple ID and password on different devices is not possible .

Alias has nothing to do with account .

The two iCloud accounts will only merge when same Apple ID and password on the same network is signed in between devices being used Mac / iPhone / iPad , and iCloud Drive , desktops and documents , the apple inbuilt applications , including keychain , safari ....should be enabled Change your iCloud settings - Apple Support

Note : you can never merge two icloud accounts with different Apple ID signed in the devices .

tygb wrote:

The two iCloud accounts will only merge when same Apple ID and password

This makes no sense. You cannot have 2 iCloud accounts on a single Apple ID. That's not they way it works. An iCloud account is either an Apple ID in and of itself, or part of an Apple ID. You cannot add a second iCloud account / email address to the same Apple ID except as an alias, which does not create an entirely new account, merely a new address who's emails are received by the iCloud account it was created in.

tygb wrote:

If there are different devices the Apple ID and its password should be differently signed in

Yes.

So according to the question merging two iCloud accounts with different Apple ID and password on different devices is not possible .

Correct, that is way I said.

You said they could be merged if created under the same Apple ID, which does not make sense. You cannot have 2 iCloud account under the same Apple ID.

an Alias is part of an account, of course it has to do with an account. An Alias creates a new email address under the same iCloud account. That is what I was trying to explain, because you said, that you needed to have both accounts under the same Apple ID.

You were mistaken or explained poorly what you meant in your first reply.

If there are two iPhones , iPhone A and iPhone B , a single Apple ID will be signed and not two , Apple ID is created on an individual device and a single iCloud account will be created on each device .

That's an assumption. iPhone A and iPhone B could be signed into two different Apple IDs, which cannot be merged.

If they are signed into the same account, there is no "merge" the data is synced between the devices logged into the same account.

You cannot merge iCloud accounts.

Best you can do, is manually move any content from one to the other.

When Apple ID say example1@icloud.com is signed in between devices pure syncing will occur , for gmail accounts syncing will not be two way ( specially for mail accounts ) .

So long as you’re signed into the same Apple ID, your devices will sync; even for Apple IDs that are gmail addresses