Filter values in forms' relation reference

[FelixHinckel]

I have a QGis project, whith a relation between an observation layer, and a list of species.

The list :

On this list, 3 protected species, and one unprotected.

The observation layer :

The observation is only described by the name of the species.

Both layers are linked by a project relation :

In the observation layer's form, the name of the species is chosen via a relation reference.

There is a filter on the relation : only protected species can be selected.

In Qgis, when I want to add an observation, I can choose from these three species :

But in QField, when I want to add an observation, the filter is not active :

Is there a way to activate the filter?
(It works for Value Relation, but I need to use a relation reference.)

QGis 3.34.6-Prizren
QField 3.4.2 Ebo (Windows ans Android versions)