Picture quality issues when streaming sports

I use the Tivimate-app and Fire TV Stick.

I’m having a major issue with the picture quality, especially during soccer matches (football).

The white lines on the soccer field look very pixelated.
Also, the stands next to the field flicker frequently.
(Otherwise the picture quality is good and I have no problems with the buffering.)

I’ve already tried activate "Auto Frame Rate" on the Fire TV Stick.
I also tried turning off the TV's "motion settings."
Unfortunately, none of this worked.

I would appreciate any help!