Got in touch with Elektron support, there’s a trimmer in order to set the brightness.
When assembled a unit could get slight different brightness due to display or simply by a different trimmer value.
I’ve not removed any film from both A4 and RYTM.
To change the brightness i should regulate the trimmer, but my A4 is 10 months old and in order to not void the warranty i should send it to their labs in Sweden: “A4 display is fine as it is for the next 2 years and 2 months :D”