What is the degree of deviation of the direction for someone far away, is it 90 or 180 degrees, and what is the evidence for that?

Those far from Mecca should face the direction of the Kaaba, not its exact spot. It suffices to have a strong presumption that the Qibla is in the direction ahead of them. A deviation does not harm as long as it does not go beyond the direction of the Qibla. Scholars have used as evidence for this the Almighty's saying: "And to Allah belongs the east and the west. So wherever you turn, there is the Face of Allah" [Al-Baqarah: 115], and the Hadith: "What is between the East and the West is a Qibla."