the behavior I seemed to observe is that mongod will ignore maxTimeMS. even if its lower than maxAwaitTimeMS it won't timeout the query. but on mongos it will hit a timeout if mongod doesn't respond before maxTimeMS. in the spirit of reducing behavior differences between replSets and sharded clusters we should fix this to have just one behavior. I tested this with 7.1 sharded/unsharded and 5.0 sharded/unsharded. and it seems 7.1 was the only one where it errored