I have a PR200 with 2 RS485 interfaces. Is it possible to read some data from a Modbus Slave Sensor over one RS485 and make them available on the other?

Yes, this application is possible.

You need two network variables, one per interface. Then you just link them by means of the tools ‘Network variable input block’  and ‘Network variable output block’ . For step-by-step instructions, please watch this video: