iMac late 2015 Could not load Security & Privacy preference pane

Hmmmm,

Are you running any VPN, Anti-Virus, or Cleaning apps?

We need to see what all is running, a report from this will not display any personal info...

Using EtreCheck - Apple Community

EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/

Thanks for Old Toad’s etrecheck instructions…

Slow iMac 2017 - Apple Community

Use the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts...

Try one of these two…

You can use Drive DX to possibly get a better view of Drive health…

https://binaryfruit.com/drivedx

Thanks to Jack-19…

It may be wise to run SMART Utility to check the drives' health.

Is the Account that you are logged into an Admin. User Account or Standard User Account...?

Only the Admin. user can make changes to the Mac's Security and Privacy Preferences.

If this account is Standard, then it can be changed to Admin. by the Admin. Account User.

see convert standard user to admin. at > Set up users, guests, and groups on Mac - Apple Support

oltíon wrote:

No VPN, even the private relay is set to off on this computer.

as per now the problem still exists.

How about any "cleaning", "optimizing", "speed-up" or anti-virus apps on your Mac?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Does anything work differently8f you disconnect from the Internet & disconnect Ethernet cable if you're using Ethernet?

How many users are defined? How many use it actively especially for accessing remotely? It’s clearly a memory issue gotten worse with a more demanding OS - both RAM & hard disk are probably getting chewed to pulp.

Your iMac is officially vintage, just a notch before being Apple declares it officially obsolete. Which could happen anytime now. Consider replacing, and plan accordingly (i.e. backup more often and start moving stuff to the cloud).

Maybe not, but that doesn’t change that it’s almost obsolete and lacking a load of fixes. Also, blank account on a fresh os isn’t a reproduction of the problem. Anyway, I have nothing more to add; all the best.