My experience connecting Tacx Neo 3M with Alpine to Rouvy is generally to change the Neo to have the white led lit, this has always worked for me.
There are occasions when it will work with the blue or green led lit, but don’t know why. Also for some reasons when riding I have notice the led colour has changed but the Alpine is still functioning.
Additionally, must add, I only switch to have the Neo white LED selected once I’ve loaded the chosen rote on Rouvy and of 23/12/2025 I’ve found no other option to ensure the Alpine functions as expected.