Yes, sieve filters do work here too.
A special user “fetchinguser” was created and is used in Imapsync as destination for mails fetched from a multidrop catchall maillbox on another server. The sieve processing is enabled in the imapsync task due to fetching “only inbox”, see also Use Imapsync to sync mail to a public mailbox? - #4 by mrmarkuz and Imapsync — NS8 documentation
In Roundcube I created sieve filters for the users, here for example for user Markus:
…and here is another example for user Buck:
This way you can add a sieve filter per user that should get mails from the multidrop mailbox.
You can check the mailbox of the fetchinguser from time to time for mails that couldn’t be processed by the sieve filters.
EDIT:
Please check the known limitations of the imapsync implementation.