It is supposedly possible to filter by shard in queries by using a specific ShardIdentifierProvider that would implement org.hibernate.search.store.ShardIdentifierProvider.getShardIdentifiersForQuery(FullTextFilterImplementor[]) in such a way that some filters would be interpreted as shard filters.
See org.hibernate.search.test.sharding.LogRotationExampleTest.filtersTest(), and more specifically org.hibernate.search.test.sharding.LogRotationExampleTest.LogMessageShardingStrategy.getShardIdentifiersForQuery(FullTextFilterImplementor[]) for an example.

When using Elasticsearch, though, such filtering doesn't work. org.hibernate.search.test.sharding.LogRotationExampleTest.filtersTest(), in particular, fails.

The main issue is that org.hibernate.search.store.ShardIdentifierProvider.getShardIdentifiersForQuery(FullTextFilterImplementor[]) seems to be ignored in org.hibernate.search.elasticsearch.impl.ElasticsearchHSQueryImpl.
LuceneHSQuery takes it into account in org.hibernate.search.query.engine.impl.LuceneHSQuery.getIndexManagers(EntityIndexBinding) when it calls org.hibernate.search.store.IndexShardingStrategy.getIndexManagersForQuery(FullTextFilterImplementor[]).