Macbook Air CPU usage issue

The usual app with that is Trellix / FireEye. If that is installed here, check for updates and then contact the add-on anti-malware app vendor for assistance, or remove the add-on anti-malware per the vendor’s instructions.

"Macbook Air CPU usage issue: [...]After a few minutes it started heating up again and 'xagt' is back at 290% CPU. How do I fix this?"

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Avoiding App Issues:

Create a Profile.

If you want to keep it installed, but not use it, then you can create a profile to block out the app from being used. In essence it would be disabled.

CREATE the New Profile:

1. Download: Apple Configurator for Mac
2. Open: Apple Configurator
3. Go to: File menu
4. Select: New Profile
5. Select: Restrictions (located on the left pane)
6. Click: Apps
7. Select: "Do not allow some apps" for "Restrict App Usage"
8. Go to: File menu
9. Select: Save...
10. Save as: MyProfile.mobileconfig
11. Save to: Documents folder
12. Close: Apple Configurator

Then...

INSTALL the profile, as I've instructed in step II. of my User Tip: How to Use a Profile to Disable the iSight Camera in macOS 15 Sequoia - Apple Community