Mostly we use all purpose flour. My wife made some donuts, did not add
Any spices, yet the donuts came out very salty, had to throw them out.
I also tried to make gravy did not use any spices, but the gravy was
Very salty too.

What is it with this flour, I know it has baking powder/soda
But why is it so salty?

Self-rising flour is a short cut for bakers. It has added salt and baking powder.

Plain All-purpose flour is straight flour.