SD is the place I would find this answer:
What is the most common protein in the Rhein region? chicken? veal? venison? something else?
I have no answer for the Rhine region in particular, but according to this statistic, pork is by far the most popular meat in Germany, and I have no doubt that this applies as well to the German Rhineland, because I don’t know of any other special meat preferences in that region.
This is the annual meat consumption per person in Germany in kilograms in 2020: 32.8 kg pork, 13.3 kg poultry, 9.8 kg beef or veal, 0.7 kg mutton or goat, 0.1 kg offal and 0.6 kg other.
Source:
ETA: of course this doesn’t take other protein sources into account, like dairy, eggs, fish, soy, lentils and so on, but I guess that meat still is the predominant source of protein here.