When HDMI cable connected, the display is fast forwarded.

Hello Memaw01,

Do you notice if this happens with all video content in all apps and websites, or one specific website or app? If the issue happens in a specific app or website, it's possible the speed can be controlled from the video player in question. You may see a clock similar icon if you move your cursor over the video. If you click on the clock icon, you should have the opportunity to adjust the speed at which the video is playing. If you're unable t adjust the speed from the video, follow the steps below to restart your Mac. While simple, restarting is a great way that can resolve many issues.

1. Click the Apple logo towards the top-left.
2. Click Restart in the menu.
3. Once the Mac restarts, log back in to your user and test to see if the issue persists.

Let us know how that goes!