Believe it or not, we are rehabbing a house here, in Oklahoma City in a neighborhood called Military Park. It has (had) knob and tube wiring that was still functional. It is disappearing although the NEC does allow for it in certain applications (agricultural or industrial). It’s addressed in section 320, 320-3 specifically. I know quite few electricians who say “leave it alone, if it’s done properly”. Now, if a person has a sensitivity to EMF they will notice immediately, as knob and tube generates a strong magnetic field.
Knob and tube can be safe, and still exists but, as a practice when we are updating a home we update the wiring, to ensure the inclusion of gfci, and afci breakers. There is no substitute for safety.