Does it still happen with hardware acceleration disabled?

With Firefox 117.0 and hardware acceleration disabled the problem is solved. (With Firefox 116 that was not the case.)

Thank you very much!

You might need to update your graphics drivers if you want hardware acceleration to work better with video. You can disable it just for video by going to about:config in the address bar and changing media.hardware-video-decoding.enabled to false then restart the browser.

The graphics driver is on the latest version according to Lenovo Vantage. But the Diver- und Support-Assistent tells me that: "A customized computer manufacturer driver is installed on your computer. The Intel Driver & Support Assistant is not able to update the driver. Installing a generic Intel driver instead of the customized computer manufacturer driver may cause technical issues. Contact Lenovo for the latest driver for your computer."

Why is Lenovo not using the Intel grafik driver?

I found a new Intel VGA driver on the Lenovo support web page and installed it. Wondering why Lenovo Vantage is not showing or updating it.

With the new Intel VGA driver found on the Lenovo support web page, the problem is gone without the need for hardware acceleration disabled.

Still wondering why Lenovo Vantage was not updating it automatically or at least telling that there is a new graphic driver is available.

The answer from the Lenovo Support Hotline, why Lenovo Vantage didn't update the driver, was really not satisfying. They said, Lenovo Vantage will only show updates when there is an issue with Software from Lenovo. As Firefox is no Lenovo software, the graphic diver was not automatically updated. That leaves me just speechless. :-(

The issue accured again with the new driver and also with hardware acceleration disabled. With YouTube videos and YouTube shorts.

Same videos are running fine on Chrome.