Screen flashes to black for 1s or more

Use another account for testing

If another user account is already set up on your Mac, you can simply log out of your account (Apple menu > Log Out) and log in with the other account. But the best way to test is with a newly created account:

1. Choose Apple menu () > System Preferences, then click Users & Groups.
2. Click , then enter an administrator name and password.
3. Click the Add button (+) below the list of users.
4. Complete the fields shown for a Standard or Administrator account, then click Create Account (or OK).

If you plan to test with any of the documents in your own account, make those documents available to the new account. Drag them to the Shared folder of the Users folder on your hard drive (~/Users/Shared). You can then move them to other folders after you log in as the new user.

Then log out of your account and log in with the new account:

1. Choose Apple menu > Log out.
2. At the login window, log in with the name and password of the new account. If you're also asked to sign in with an iCloud account or Apple ID, skip that step.

Now try to reproduce the issue in the new account. If you need to set up an email account or other account in order to test, you can do so.

If the issue doesn't happen in the other account

If the issue doesn't happen in the new user account, the issue is related to the settings or files in your own account.

If you need help with a specific alert or issue, search the Apple Support website for the text of the alert. If the issue happens in only one app in your account, it might be related to one of that app's settings. Check the app's documentation or support website for help.

You can remove the new user account when you're done testing. Follow the steps for creating a new account, but click the Remove button (–) instead of the Add button (+). Before removing the account, make sure that you don't need any of the files or settings you created or copied in that account.