Hello,
I have two networks:
- first network connection is a 1Gbps fiber
- second network connection is a 10Gbps fiber

temporarily (waiting to upgrade both network to 10Gbps) I have to connect the two.

Is there a way to use a Mikrotik (I have a CRS326-24S available) to act as a "media converter"?

Using a 1Gbps transceiver on one port and 10Gbps transceiver on the other port, what I have to configure to allow all traffic pass through the connection?

I want that all traffic pass just like it was only one cable.

Can I use a bridge? An interface bonding in broadcast mode?

Or I'm completely off track....

Thank you

If it passes from SFP to SFP+ ports then it behaves as a "media-converter" already. Have you checked this or you ask in advance?
Any switch is a media-converter if port speed you treat as a different medium.

Thank you for you quick reply.
What I don't understand is: what is the configuration that I have to apply to this two ports?

One fiber cable is inserted in a 10Gbps transceiver (the cable that at the other end has a 10Gbps transceiver)

One fiber cable is inserted in a 1Gbps transceiver (the cable that at the other end has a 1Gbps transceiver)

I wish that the two peers pass all the traffic just as if they were connected directly.
I don't know what is the better configuration on Mikrotik: bridge? Interface bonding?

I want that all traffic pass (vlan, ecc..)

There is no way to connect ports "directly", traffic always flows via some "switching device" as both ports are connected to it and that device makes medium conversion. There is no short-path. I have no CRS handy but if we talk in ROS wording then you should use bridge as bridge is the contemporary name for virtual switch in ROS. in SwOS there is no need to bridge anything as switching traffic between ports is built-in function of a switch.