Using this as the reference point,

https://docs.mongodb.com/manual/reference/operator/aggregation-pipeline/

Compass seem to be missing these commands in the dropdown list in the Aggregations tab:

$listSessions

$merge

$planCacheStats

$replaceWith

$set

$unset

And, this Aggregation Pipeline command exists in Compass only, but its documentation cannot be found on the website.

$searchBeta