How can I fix the image printers on the TV?

I recently got a Grundig Alexa-fire-tv. The purchase was a bit hasty, I have to confess, because I don't have a contract to watch Wi-Fi TV. With my previous TV, I didn't feel it was necessary. I just looked at a few things via HTMI cable on my notebook. And that worked just fine. Now when I do the same thing I sometimes have violent image jerks. Especially with Firefox. This is definitely not due to the HDMI cable, because it looks really thick and solid. Maybe someone would know a solution. Thank you

Something else in the context. I have been under contract with Vodafon for over 5 years now with a combination package (landline and internet 16kb). Now I'm considering switching to Telekom if my contract expires in 6 months with timely termination, and then conclude a 3-pack with Magenta at Telekom. Would that be a smart option? Maybe someone can help me there too.

As far as the image printers are concerned, I'm unfortunately out. I suspect that it could possibly be due to the HDMI standard or possibly the HDCP copy protection. But that just got blue.

I can help with the potential switch to us.

Is the "plan" ready for a decision? Should there be a complete change, i.e. With number portability, etc?

Regards Daniel H.