Hi and welcome to the RME user forum.
I do not own an Apple computer, but I found a video for you which could be of help:
Under Logic -> preferences -> devices: did you select the proper RME driver? Which driver did you install?
On the track that you want to record: did you select the correct input channel for SPDIF in the channel strip, see video at 1:40?
Rest up to the Apple experts
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13