There are very few actions which can outright be declared mortal sins. Situations and culpibility are real things.
If a healthy, fit, 20yo man, Joe, lives next to church and is too lazy to get out of bed to get dressed and walk next door, then yeah, it’s a mortal sin. But in the apartment above him, Sam also 20, lives–but isn’t really “healthy” because suffers from severe depression or agoraphobia. Then his watching Mass is not only not sin, it’s likely highly favored and blessed by God.
When I just had my infants, the first week, I did not attend Mass. My obligation was completely wiped away. I did not view Mass on TV. I was tired and not really up to it. On Easter, however, when I am exempted from Mass because of a life-threatening severe allergy, I do try and view a Mass online while my husband attends because I am physically well enough to attend but have a medical reason that I cannot that dosn’t stop me from living the rest of my life.