Admin privileges not working on one account

I can't confirm this theory, but as I have seen similar reports with various software, I think the developer's are doing something stupid like looking for UID 501 and just failing the install if they don't see that.

That is the first user created and they may have some misconception that it is the only "admin" account.

You can test to see if your account isn't somehow misconfigured by entering a command in Terminal using sudo:

sudo ls ~/

sudo is substitute user do. ls is List and ~/ is your home directory.

If your account is properly configured, it will ask for you to enter your password. If it allows you to enter the password, then your account is fully "admin" capable.

See this article Set up users, guests, and groups on Mac - Apple Support

• 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. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.
• Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.

Convert standard user into an administrator .

1. Choose Apple menu > System Preferences, then click Users & Groups.
2. Click the lock icon to unlock it, then enter an administrator name and password.
3. Select a standard user or managed user in the list of users, then select “Allow user to administer this computer

If you are signed in with the primary account , log out from this account and sign in with the other account that you have created ( it could be admin / standard ) and select the primary account and click on subtract sign , check the box of delete home folder ( the last option ) and click on delete button .

But your primary account has corrupted data if you use shared folder method ( copy and paste ) then in new admin account it will then corrupt this account also .

And you are avoiding time machine back ups also .

And what certain programs apart from inbuilt apple applications are you planning to install that plays a role ( could affect the system performance ) .

Yes as the first admin ( is corrupted ) if you use shared folder ( copy and paste method ) , it could corrupt the new user account also , so why not try time machine method .

Regarding mails , they are saved on the server so will not be lost .

I'm confused as to your answer. I thought the account was admin capable. Regardless, if you make it admin capable and sudo works, it should be able to install software.

Since it installs on two other accounts, something must be amiss with the account. I don't know what it would be.