Is it possible to deploy QinQ VLAN inside ELTEX?

Question

Computer networks

I don’t understand something, there is incoming traffic with different VLANs wrapped in a QinQ tag, let’s say 999.
I can’t receive this traffic on the switch port and deploy it to VLANs that were inside 999.
Is this even possible?
A large number of VLANs can walk inside 999.
All this is easily done in the opposite direction - when many different VLANs come to the port, and I wrap them in 999, and already start up 999 on BRAS. And vice versa? That is, I need to deploy all these VLANs inside Eltex.
I of course implemented it through one place like this:
I set SNR, received VLAN 999 on one port, deployed them on another port with mode access, from which tagged VLANs flew that were inside 999, then from this second port I plug the patch cord into the same switch already in the third - trunk port, and now inside the switch I can see poppies from all VLANs that were inside 999, and everything is sorted out (by their VLANs).
But that's an ass. Pulling the patch cord out of the switch and inserting the same patch into the same switch is generally nonsense in my opinion.