brush tracer on canvas will not show up.
*** Bug 389088 has been marked as a duplicate of this bug. ***
You're not giving any information that would make it possible to help you. Not the operating system, not the version of Krita, not a real description of the problem!
Fortunately, I have second sight, and this link will most likely help you out: https://docs.krita.org/KritaFAQ#Krita_starts_with_a_black_or_blank_canvas_and_nothing_changes_when_you_try_to_draw.2Fshows_a_black_or_blank_screen_on_my_Windows_system_with_an_Intel_GPU
*** This bug has been marked as a duplicate of bug 360601 ***