Hi!
I don’t know if this technique is documented or written here in the forum, but just in case I’ll share it with you.
It is about recording external sounds on independent tracks and applying internal effects and modulations on the OP-1 Field. For this I am using the Vocoder, and selecting the line audio input in mono or stereo. In the vocoder I turned the orange dial to the left where the orange dot appears to hear the clean input and applied a long curve to the envelope of the vocoder effect to minimize its superimposed sound. In this way we have a pseudo auxiliary input with effects and direct modulation to each track.
I hope you understand my explanation and if it has already been documented, excuse me. I see many posts of people explaining how to process external signals by making recordings on tracks free of what is heard with the effect of the master but it can be done in a more direct way.