Could it be possible to emphasise (other color etc.) the line now playing track in the list of tracks. I didn’t find any settings that would do that. If it exsists please tell me where can I find it? Here is a picture of a true situaton. Of course I can see what is going on because at bottom of the screen is the track that is playing. Anyway I think that it would be more informative if the track in the list would be emphasised.
Not sure to understand what you mean, but if you want to see the playlist you need to open the bottom bar then click the playlist button there the active song is clearly visible 
Library browsing and media playing are not related.
It’s as hard to me to understand what you mean because I’m the user and you are the programmer but I try to explain and this will be very difficult. My suggestion has nothing to do with playlist. The picture that I put into my first mail was a list of tracks that I was playing from one album, had nothing to do with playlist. Perhaps we understand playlist differently. If you look to the bottom of the picture you can see that track one is now playing. And other tracks of this album are above that. It would be very nice and visual if the track that is now playing, in this case track number 1, on the topmost positon of the tracklist would be emphasised for example with another colour. And I underline that it would just be very visual thing not in any means necessary. I’m quite sure that you have seen players that function just like that.
Actually no most players works like Yatse you can browse the library and play/queue things but the library does not show what is current playing as they are unrelated and would have high performance impact.
What is currently playing is tied to the actual player playlist, and the active songs is clearly indicated there see below screenshot.
Press the bottom bar or swipe it to see the player then swipe up or press the playlist button to actually see the player playlist and the queued items and the active track with a nice animated visual indicator of the current one.
