With the current release of Cumulus (3.7.7) it is only possible to filter outgoing VNI advertisements.

When specifying the same rule ingoing, all VNI advertisements are blocked.

This is a known issue, see https://github.com/FRRouting/frr/pull/4078/files

I contacted Attila and Sharpd about it on slack: perhaps the MR will get into 3.7.8 or 3.7.9