Cube Black+ currently unusable with PX4?

Dear all,

First of all, I am quite new to these subjects so I apologize if my questions are irrelevant or inaccurate.

First, the context (in case you notice that I am doing it wrong - skip to the bold part if it seems irrelevant) :
I am willing to use a Septentrio card (AsteRx m3 pro+ with 2 antennas) with Pixhawk Cube Orange with PX4 pro using SBF stream since NMEA stream seems to not work properly.
As far as I understand, it is needed to use a custom fmu version to be able to chose “SBF” protocol in “GPS_1_PROTOCOL”. To do so we saw that fmu v3 was compatible with Cube Black, so we decided to buy one except that now there is only Cube Black+ that is sold.

We have bought a Cube Black+ and tried to make it work with our Pixhawk 2.1 board and PX4 Pro with QGC but none of the versions tried (custom or stable) succeed to be upgraded so I wonder if it is even possible since I do not find anything about it on Internet.
Thank you in advance for you return with any lead you may propose, I remain available for any further information.

Best regards,