Wherever a time signature appears, the staff lines behind it are ever so slightly thicker. I also notice a little bit of the key signature before it and the note or rest after it is a little bold. This is not visible on the screen (it’s very slight), only on the printed page. (Shown below)
I changed the staff line thickness to “0 space”, which makes all the staff lines a little thinner, including behind the time signature; but the end of the key signature and the first note or rest is still thicker (I didn’t include a picture of that one)