I want 2 Apple Accounts on the same device.

You can only use one account on an Apple mobile device with some exceptions:

1. In Mail if you want to use a different, or more than one, iCloud account. Settings -> mail -> accounts -> add account -> iCloud

2. Messages and Facetime. Sign into a different Apple ID for these services in Settings. Note this has to be the same ID for both. Go to Settings > Messages > Send & Receive, and make sure both your telephone number and Apple ID are input there and both show a checkmark. If you need more help, check this link: Add or remove your phone number in Messages or FaceTime - Apple Support .

3. In the support article: If you subscribe to Apple One and use a different Apple ID for iCloud - Apple Support Apple alludes to using a different Apple ID just for media, subscriptions, and purchases, but doesn't describe how to do this. See if these work:

In iOS/iPadOS: Go to Settings > [your Apple ID] > Media & Purchases. Sign out of the current ID and sign in with a different one.

In Ventura or later: First, quit Settings. Then, in App Store, choose “Sign Out” in the Store menu, then click on the “sign in” button that appears in the main window. You can then sign into the other account. (from: Using different Apple ID for media & purc… - Apple Community )

4. Use a different Apple ID to share purchases with Family Sharing as outlined in Use a different Apple Account to share purchases with Family Sharing - Apple Support

Apple has no formal account merging or transferring process. If you want to condense the two accounts let me know and I can post instructions for how to try to do the best you can .

Sorry but an iPhone is fundamentally a single-AppleID device. (as is an iPad)

There’s no practical way to routinely “swap” between AppleIDs.

Is there a compelling reason why you don’t want to sign-in your new device with your old — pre-existing — AppleID ?

(That’s certainly the “least friction” method and also the way Apple’s ecosystem is generally intended to operate)

Manage and use your Apple Account - Apple Support

If so, post back as there ARE “Multi-AppleID” alternative — each with different pros and cons — which might fit your specific needs.

My post already told you how and where it can be done.

The main problems are where purchases are concerned. Any apps downloaded with an account are permanently tied to that account. If you later change the account used to download them you either have to set up family sharing between the accounts or you have to re-purchase the app. You can sign in with a different account on the entire device but then there's a 90 day wait period plus other issues which basically mean it is a real pain to do it that way.

So let's say you decide to use a different account for just apps and media purchases. If you later decide you do not want to use that account, all the apps on your phone now won't update anymore unless you buy them again.