[lightsout]

i have read on several websites that the deinterlacing quality of the shield should not be very good, e.g. in the nvidia forum or in the kodi forum

https://forum.kodi.tv/showthread.php?tid=343959 

Maybe you confused that with it's upscaling ability? On the previous models it was a notch behind the competition. This has been remedied with the new model. 

Well not totally because there are still some AI upscaling limitations, especially for those that watch broadcast interlaced TV:

2019 Nvidia Shield Ai upscaling settings (click)

But much better vs the non 2019 Shields  

From the comparisons I have seen. The new basic is the same and the 2017 model, the new enhanced is comparable to competing products. And AI is something else. 
I believe enhanced mode works all the time.