When I was leaving Amazon, the logic was generally -- don't go to the same org in a different company. E.g. if you work in S3, don't go to Google Cloud Storage. If you land in ads or maps or search or whatever, that should be fine.

Though, it's really up to Amazon whether they want to keep you unemployed for 18 months, which is (in my mind) totally unethical to even have in the contract in the first place.