Can I have multiple Apple IDs signed into iPhone?

Yes, but only one primary one which will apply to most services. As you can tell from the different basic Yes/No replies, it is easier to properly address an issue if we know your objective.

There are several likely places where you can use a different Apple ID:

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 & … - Apple Community )

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

No. That's when you start running into issues as described in: View and remove your devices that are associated with Apple ID purchases - Apple Support - Read "More about associated devices" at the end where it refers to the 90 day wait. This applies to re-downloading past purchases (you can make new purchases), automatic downloads, and iCloud based services such as Family Sharing, Match, and Apple Music.

If you want to have that music then either set up Family Sharing with the other person or buy your own copy of the music. To learn how to set up Family Sharing, read this support article --> Set up Family Sharing - Apple Support

- Only lists doing this on an iPhone, iPad, iPod touch and Mac.

No. If you wanted to do this for the entire phone you would first erase the entire phone, then sign in with the other account. If you wanted to do this only for the app and media stores you would need to sign out of those and then sign in with your other ID and password.

Again remember that you may encounter limits. Apple's way (and this is not Google) to accommodate multiple accounts is to do so through Family Sharing. That way you can legitimately use licensed items purchased with other accounts.

Some of this is getting repetitive. ;-)

iPhones are primarily single user account only, except for the few places where you can use a different account for a particular service. As far as apps are concerned they should only all be downloaded with a single account. You could in theory download them with different accounts but it will be a big nuisance trying to update them. You have to be signed into the store with that particular account, plus you may find timer restrictions prevent you from changing accounts too frequently (I presume to discourage people from pirating software from friends).

No. iDevices are single user devices.

Here’s my use case if it helps anyone. You can have two Apple IDs that you frequently switch between in the App Store. It won’t allow a third. I run into this because I’ve lived in three countries and I had to have three separate Apple IDs in order to download geo-restricted apps. When I need to update, there are always apps that I can’t update because they’re from the third App Store. I need to go through a horrendous recovery process to sign back in.

It's the main one signed into your iPhone for most things. It is for everything unless you specifically go in and change the settings on one where that is permissible.

iCloud specifically is a series of services; the App Store is another as is Apple Music.

Which iCloud.com features are available on your device - Apple Support

https://appleid.apple.com/faq

I want to separate devices can I set up separate apple ids to keep all separate. My attorney advises. All companies need to be separate. I am an apple guy but I need to be bulletproof. Suggestions

With many large companies under one umbrella I was advised that setting it up as a family my be the answers. After further research I have found that does not meet our needs any suggestions.

So do you have any suggestions.I am also worried about hackers fraud and data safety

Apple forces you to have different IDs if you purchase software in different countries, but then also tries to force you to only have one ID. How well this works on your device changes every time time the OS updates. But quite often I seem to have more than one ID signed in on some devices, though not others. I live in Germany but have lived in the UK and US (simultaneously, for work) and right now my UK purchases work on my iPad but not my iPhone, both updated iOS, and both at least nominally logged in to my German account.