Probably very few will agree with me, but IMO excellent is Dvoretsky's Endgame Manual.
People disagree because they say it's too advanced.
But if you only do the blue diagrams and blue text then it's accessible to practically any level.
It's not a waste of money either. There are over 200 blue diagrams, and you can use the rest of the book (the black ink) as reference material.
Opposite colored bishops, fortress, etc.