public List<OffsetFetchRequestData.OffsetFetchRequestGroup> groups() {
        if (version() >= 8) {
            return data.groups();
        } else {
            OffsetFetchRequestData.OffsetFetchRequestGroup group =
                new OffsetFetchRequestData.OffsetFetchRequestGroup()
                    .setGroupId(data.groupId());

            if (data.topics() == null) {
                // If topics is null, it means that all topic-partitions should
                // be fetched hence we preserve it.
                group.setTopics(null);
            } else {
                // Otherwise, topics are translated to the new structure.
                data.topics().forEach(topic ->
                    group.topics().add(new OffsetFetchRequestTopics()
                        .setName(topic.name())
                        .setPartitionIndexes(topic.partitionIndexes())
                    )
                );
            }

            return Collections.singletonList(group);
        }
    }
Indicates that it is not possible to fetch consumer groups in batches with FetchOffset.
Instead consumer groups' offsets must be fetched one by one.
clients/src/main/java/org/apache/kafka/common/requests/OffsetFetchRequest.java