I’ve just tried this on my Samsung UE32J6300, software version 1530, NowTV App version 4.3.19, with the iPad app (126.96.36.199 running on my iPad Pro 9.7” on iOS 12.3.1) and the Android app (188.8.131.52 running on my 1st Gen Moto G Android 5.1).
Everything works perfectly, with OK signified by tapping the centre of either Trackpad or Directional Arrows. (There’s nothing actually marked OK, in either of these, on either the iPad or the Android version - is this what you find also?)
What are your model and version numbers compared with mine, for TV and Android devices and apps?
I did wonder about the two modes, so I was careful to try both, on both Android and iPad, and all 4 options worked fine.
While only NowTV has this problem, for you, it does seem that it can further be narrowed down to something about the version of the TV, or the NowTV app on the TV, or the version of Samsung Smart View, or of Android, on your sending device.
Same SmartView; different Android which may matter; different TVs, which may not.
So knowing which version of the NowTV app is in use on your TV is probably significant, as I suspect this is where the trouble might lie. And can you update it from the Samsung Apps store on the TV?
As for the Android version, do you have any other Android devices you can try? My Moto G and it’s Android are rather old, but I’ve got a Nexus tablet somewhere I can dig out and give this a go on.
How do you ‘lose’ a Nexus? I know it’s in my study somewhere... 😞
I guess your workaround for the moment then, is to use Directional Pad.
As a last despairing test of Trackpad though, what happens when you rotate your phone from Portrait to Landscape and try it? And then the two further 90 degree rotations?