AWS Glue surpriginsly does not support reading NDJSON out of the box. You have to create a custom classifier, but it is incredibly simple.
Use the pattern
$[*] with a custom JSON classifier and it should read the NDJSON schema more or less correctly.
NOTE: Editing classifiers doesn't seem to work well, or they are denormalized in the crawler. Instead, delete and create new classifiers when making adjustments.