How do I change admin user of my Mac running macOS Sequoia?

The first admin account created on a Mac is both an Administrator and the sole Owner. I have never seen a method to make a different account the Owner.

Read this for further info about Ownership: Ownership means two different things in Macs: how to tell them apart

I believe you are headed for a complete wipe & reinstall. At this point, having removed the first Admin account, your Mac is in a certain state of limbo. IMHO one should *never* attempt to change or delete the first Admin account on a Mac. Too many potential problems.

As Mentioned earlier

The Original Owner / Admin account on Apple silicon computer Has ownership privileges that are stored in the Secure Enclave of the machine

https://eclecticlight.co/2021/07/18/last-week-on-my-mac-the-perils-of-m1-ownership/

As far as I can see

You are better to be prepared to Start Over from Scratch

Erase your Mac and reset it to factory settings - Apple Support (CA)

In trying to change user accounts, I ended up disconnecting my external drive that had Time Machine backups, then went into recovery mode and erased the Mac hard drive. Reinstalled Sequoia, reconnected my external drive and migrated that data from Time Machine. That way I was able to establish new user accounts as an administrator, one which I use all the time, the other as a backup.

omits wrote:

Supposing I recover that account from Time machine. Will that restore things somewhat.

Restoring the account's home folder is possible but I'm not so sure about the account itself. You could try, but be prepared for it to not work out.

If it were me, I'd wipe the system and reinstall from scratch. @leroydouglas provided links for how to do that.

omits wrote:

This is the original Admin User when I got the Mac. (Mac 14" M3 Sequoia 15.6.1). The user account has gone but the folder(s) remain. Note this is the "owner" user and noted above. I have a new Admin user from which I am removing said User. The error is "Unable to delete the User account xxxxx" An error occurred while deleting the user's Home folder. Error 513. I assume that the new Admin needs to be configured as "Owner" now (automatic)?

Advice sought before I attempt just dumping them.

Not sure what was done or not done....

ref: What to do before you sell, give away, trade in, or recycle your Mac - Apple Support

ref: Erase your Mac and reset it to factory settings

omits wrote:

Thanks. I'll keep an eye out for problems. My fault. Still think a warning is needed if Owner account remove is attempted.

Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators.

The implications being.

The Original User Account ( Owner/ Admin ) Account can add, delete, elevate or demote Other Added Accounts

Nowhere do we see the ability to delete or expressly intend to remove the Owner / Admin Account

As for " warning is needed if Owner account remove is attempted. "

To use this analogy related to the Law

" There's an important legal principle that says “ignorance of the law is no excuse.” "  you can't defend your actions by arguing you didn't know they were illegal, even if you honestly did not realize you were breaking the law. "

The upstart being

Know what you are doing before attempting such actions

If unsure, ask before rather than afterwards

All to often, we can avoid such unfortunate incidences by seek the advise and experience from others

omits wrote:

• Install all macOS updates, security patches, and major upgrades — these do not require the original "Owner" account or access to the Owner Identity Key (OIK).

Just so you are aware, that's a grey area. Some users have reported difficulty installing macOS updates & upgrades using an account that is not the Owner. Also, full stop installing macOS on an external drive. YMMV.

omits wrote:

There are plenty of warnings in our digital devices,

Agreed

some inane, some useful.

Agreed

that would be a useful one IMO. 'I rest my case'.

The error that was performed, through a lack of / or though not knowing, dovetails into the earlier posting