iMac keeps freezing and restarting even after restore and updates

Please download and run Etrecheck.  The free version is sufficient.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Check Etrecheck's Privacy settings and make sure the checkbox for full disk access before running:

Then we can examine the report and see if we can determine the cause of the problem.

Hi,

We need to know whole kernel crash log and other diagnostic informations which are located at the directory /Library/Logs/DiagnosticReports/.

You can paste whole log with "additional text".

First, let’s see if this issue happens in Safe Mode:

1. Shut down your Mac.
2. Press and hold the power button on your Mac. As you continue to hold the power button, your Mac turns on and loads startup options. When you see Options, release the power button.
3. Select your startup disk. It's named Macintosh HD, unless you changed its name.
4. Press and hold the Shift key, then click the “Continue in Safe Mode” button below your startup disk.
5. Log in to your Mac. You might be asked to log in again.

NOTE:

If the strange behaviors do not occur, then it may possibly be a software issue.

If the issue doesn't continue in safe mode:

Leave safe mode by restarting your Mac normally, then try to reproduce the issue.

If the issue doesn't return, it might have been resolved by the other things that safe mode did at startup, such as checking your disk and clearing caches.

If the problem persists, then let’s try this:

• Software Update.
• Use Apple Diagnostics to test your Mac.

Need more help?

• Call 1-800-APLCARE.
• Contact Support.
• Mac Support.
• Mac User Guide.

All the best! 👋🏼😉

Check the power cable on the back of the iMac and at the wall socket to make sure that it is tightly connected.

Then run the Apple Diagnostics Test, as per > Use Apple Diagnostics to test your Mac - Apple Support

I strongly suspect the issue is the Máxima seguridad that is installed. If this is any type of third party:

• Antivirus
• Cleaning
• Security
• VPN
• Maintenance

app then my certainty goes way up that this is the cause of the problem. To test it, please. uninstall Máxima seguridad and then restart in Safe Mode and then restart normally. Then run a new EtreCheck report and look through it to see that there is ZERO evidence Máxima seguridad is installed. If it still shows up, then it's not uninstalled!

After you are 100% sure Máxima seguridad is gone, test your computer about 3-4 days and see how it does. If performance returns to normal then you know it was Máxima seguridad.

It just means "Full security".

Change security settings on the startup disk of a Mac with Apple silicon - Apple Support