A black line on my father's toe nail.

We observed a thin line on my father's toe nail a year and a half ago, We didn't have any clue about it so we ignored it ,few months ago my father was diagnosed with papillary renal cell carcinoma, and the fear of Cancer haunts me every night. When I read about this line causes and the highlighted words "Sublungal melanoma" I can't explain the situation to any one , I went to many doctors and I equally respect them all, someone told it's common in India some even scolded me not to search on internet ,some told there is changes you can do biopsy others told to observe.I being just a college boy , I am literally confused what to do and what not to do.Many doctors got annoyed too for me overthinking about it but only I know how everyday feels like.I am attaching a picture from last year to now.I need your advice 🙏