Currently, as far as I understand, list properties are indexed as a whole not element-wise. On the other hand, objects can be index by their contents (using BY KEY or BY VALUE), see https://docs.arcadedb.com/#SQL-Create-Index .
So I would like to propose to enhance indexing a list by item (for example noted by BY ITEM in the CREATE INDEX command).

This feature seems to have been scoped for OrientDB, too, see:

• index on embeddedlist (array of objects) orientechnologies/orientdb#4976
• Support indexing embedded types Lists/Objects orientechnologies/orientdb#5201
• Support for indexes on fields of embedded properties type like EMBEDDED/EMBEDDEDLIST/EMBEDDEDMAP/EMBEDDEDSET orientechnologies/orientdb#7093

and is also a feature in other NoSQL DBMSs:

• CouchBase: https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/indexing-arrays.html
• MongoDB: https://www.mongodb.com/docs/manual/core/indexes/index-types/index-multikey/create-multikey-index-basic/