Spellchecker often wrong!

I searched on how to turn off spellchecker because it is constantly dubbing in wrong words and changing what I type. I know what I type and I know what I want to type. Often, Spellchecker will persist and keep “correcting” what is not wrong to begin with, and I have to stop, backtrack, and override it.

Is there any way to shut it off? It is creating a lot of work for those of us who have been expert typists for decades. (This is occurring in most if not all apps.)