__consumer_offsets is used to store information about committed offsets for each topic:partition per group of consumers (groupID).
It is compacted topic, so data will be periodically compressed and only latest offsets information available.
_schema – is not a default kafka topic (at least at kafka 8,9). It is added by Confluent. See more: Confluent Schema Registry – github.com/confluentinc/schema-registry (thanks @serejja)