Firmware version N950USQU3CRC2 is now rolled out by AT&T for the Galaxy Note 8 over the air. It weights 1.4 gigabytes - it brings in a whole new OS, after all - so make sure your phone is powered up. If you wish to do so, you can try to download the update manually; just go to Settings and Software update.
Every US variant of Samsung Galaxy Note 8 is getting Oreo in the next 2 to 3 weeks
Samsung Galaxy A6 and Galaxy A6+ (2018) will not be released in the USA