iMac login is very slow

If you have done so you might want to create a new user account in users and groups in System Preferences and see if the new account has the same problem (But when you do so make sure you give it Admin Privileges). It does sound like a App is hanging on start what Apps do you have starting on log on? And do you have a Anti Virus App? Because you stated that it started just fine in Safe Mode and Apps do not start in Safe Mode.

Try removing the Configuration file...

To remove a configuration profile in macOS:

1. From the Apple menu, select System Preferences....
2. From the View menu in System Preferences, select Profiles.Note:
3. Profiles won't be visible until you have at least one profile installed.
4. Select the profile you want to remove, and then press the - (minus) button. Click Remove to remove the profile.

Next step...

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches, so if Safe Mode works try again in regular boot.

Good suggestion! :)

Delete these files& restart...

/Library/LaunchAgents/SwapperUFi.plist

~/Library/LaunchAgents/com.adobe.ARM.***.plist

~/Library/LaunchAgents/net.tunnelblick.tunnelblick.LaunchAtLogin.plist

~ tilde indicates hidden Home Library.

Apple hid the Users' Library folders...

Method 1:

1. From the Finder, select the Go menu at top of the screen, and choose Go to Folder.
2. In the window that opens, enter ~/Library, and click Go.