السلام عليكم ورحمة الله وبركاته احسن الله اليك Am I right in quoting Shaykh AbdulAziz Rayyis saying you can pray within 90° of the qibla (so facing the qibla within 45° deviation on each side being acceptable). If this is the case, is this: excused, completely allowed, or only allowed with شروط?

For a person far from Makkah, the qibla is the general direction of the Kaʿbah, not its exact point, because the Prophet ﷺ said to the people of Madina: ما بين المشرق والمغرب قبلة (reported by al-Tirmidhi; graded sahih by al-Albani raḥimahullāh). Facing within that direction is valid and not merely excused, because Allah made the duty for those far away the direction itself, as Imam Ibn Uthaymin explained. Do not fall into waswas and digging too deep.