I would like to have an option to propagate favorites from TIDAL to Roon in a way to have a heart icon applied in Roon, not just to appear in your collection.
For albums it is bearable as it is, but for tracks you lose important information (there is some reason why you made a track your favorite on TIDAL) as liked tracks get lost among all other tracks from liked albums.
How do you think that could work. A toggle switch in roon that says add all tracks to 
from now on?
That would be a proper solution, but could be confusing if likes (hearts) from Roon wouldn’t be propagated back to Tidal.
As far as I’m concerned, I plan to switch entirely to Roon and I won’t care about the state of my collection on Tidal, so, I would propose a much simpler solution - a button (or hyperlink such as “Sync Library Now”) in Settings/Services/TIDAL that would perform that only on request.
Hopefully that makes sense.
What would the button do? Add every track from Tidal to favourites () in Roon?
Almost - it would add every track from Tidal that is marked with heart to favourites in Roon.
To be precise, OP wants every TIDAL-favourited track to become a favourited track in the Roon app; not all tracks in all albums. It’s not possible to do this easily now.
In meanwhile, I’ve put all my favorite tracks (marked with heart) in a huge playlist, transferred it to Roon and now there isn’t an option to mark them with hearts… How to do it?