Screen flickers black at random times ProBook 450 15,6

[Exception2621]

Hello everyone,

i have the problem, that my laptop screen flashes black at random times. Each flash lasts approximately about half seconds. There are days on which i can work normally with the laptop - but on other days is flashes constantly every few seconds. There are no errors in the windows event log, i also made a full hardware test (F2 at start) - without any problems.

Things i tried but didn't change anything:

• Restarting Windows
• restarting graphics driver when flickering with: Win + Ctrl + Shift + B 
• Update Graphics driver to the HP provided one (back from 2023)
• Tried the newest driver (installed via Intel Graphics Software)
• Reset energy saving settings windows
• Tried many different combinations of option in the Intel Graphics Software
• Bios update
• Bios reset
• Disable anti-virus-protection

The problem occurs while battery usage and also while laptop is powered via the USB-C cable. Also the position of the display doesn't has any impact! The laptop is two years old and has no visible physical damages. 

Interestingly when i have a external monitor connected (either via HDMI or docking station) there is no flickering on the external monitor.  If the graphics card would be defect, then the external monitor should also flicker...

The HP Support Assistant doesn't show any problems and says that all drivers are the newest.

I'm slowly getting desperate because the laptop is unusable when the flickering occurs.

Thanks in advance for you help!!

CPU is 13th Gen Intel(R) Core(TM) i5-1335U with integrated graphic card.