serverStatus().metrics.query maintains counters for how many queries used which query framework (classic, SBE, or CQF). When a serverStatus command is issued to a mongos, these counters are always 0.

This is because these counters are incremented in the getExecutor() codepath which is not run on mongos, but rather on each individual shard/mongod. Thus when mongos receives a serverStatus command and consults these counters locally, they are always 0 since they were never incremented.