How is it a Torah prohibition to ride in a car on Shabbat if a Non-Jew is driving if cars were not invented at the time of the giving of the Torah. Is this actually a rabbinic prohibition instead? Are the rabbinic halachot less important than the Torah or biblical halachot?

Lets rephrase the question and give an answer: Is it prohibited under Torah law to plant an apple tree on Shabbat when these seeds did not exist when the Torah was given? Obviously it is prohibited. The Torah teaches principles and instructed those heavily involved in Torah learning, including the greatest sages of each generation, to analyze and understand those principles and then apply them to other situations, including new cases and new inventions. In point of fact, riding in a car driven by a gentile violates a rabbinic injunction, not a Torah one. Is this actually a rabbinic prohibition instead? Are the rabbinic halachot less important than the Torah or biblical halachot? This question is also mis-phrased. Indeed it is less of a violation for someone to violate a rabbinic injunction then a Torah law, but I would not say that that makes it into something “less important.” All aspects of Torah are important. The key difference is that the Rabbis, when creating rabbinic injunctions, also allowed for relaxing those injunctions under extenuating circumstances, such as major financial loss, or illness. But this is not an absolute rule, and one needs to pose a question from a competent authority. Which probably means that you had a follow-up question. Please ask it.