Window flashes/appears then disappears periodically (after Windows 11 install)

Hi xicus, welcome to the Microsoft community, my name is Bruno Leonel, I am happy to help you.

I understand that you are having problems regarding the Windows 11 window blinking approximately every 1 hour and I am sorry for this discomfort. Initially I suggest a few steps below.

First, I recommend that you check and run any pending updates on Windows Update, please:

Windows+I > Windows Update > Check for updates.

Check if the problem is resolved.

Step 1

Try performing a clean boot and see if the message remains:

1. Press Windows+R keys to open the Run Menu;
2. In the Run Menu type Msconfig and click Ok;
3. On the General tab, click Normal Startup;
4. Click on the Services tab and select Enable All;
5. Enable the option Hide all Microsoft services and click on Disable all;
6. Click Apply > Ok.

Disabling 3rd party services in Task Manager:

1. Press CTRL+SHIFT+ESC and click on More details;
2. Click Start tab and disable all programs manually;
3. Close Task Manager.

NOTE: This procedure disables all third-party services and programs. You can later, if the problem is resolved in this way, enable the programs and services that will start with Windows selectively, rather than having them all disabled. If the problem returns after activating the startup of a specific service or program, the problem is exactly in the startup of this software and it is recommended to remove it.

step 2

Using the Windows Disk, Files and Image Fix Tool

1. Press Ctrl+Shift+ESC, click File;
2. Click Run New Task;
3. Check the option Create this task with administrative privileges;
4. In the open field, type cmd, then click OK;
5. Run the following commands, one line at a time, followed by Enter:

dism /online /cleanup-image /CheckHealth

dism /online /cleanup-image /restorehealth

sfc /scannow (I know you have already executed as mentioned in the question, but I ask you to kindly execute it again after executing the 2 codes above.)

step 3

Create a new user account and check the behavior.

1. Press Windows + R keys;
2. Type control userpasswords2 and press ok;
3. Click on the Add option;
4. Select the option Do not sign in to a Microsoft account;
5. Choose a name and password for this profile and then proceed to the next steps;
6. After the new profile is created, go back to the User Accounts screen, click on your user and then on Properties. Select the Group Membership tab;
7. Mark the profile as Administrator and click on Ok;
8. Sign in with the new account. If the issue is resolved, copy and paste the files from the old account to the new account (Go to File Explorer > This Computer > C: > User > User Folder).

After migrating your data, delete your previous user: Press Windows+R keys, type netplwiz and click Ok. Select your previous user and click Remove.

If the answer helped in any way, please mark it as an answer, if your question has not been solved, please post again.

I hope I helped, see you later!