On a Dalio youtube video The following video https://www.youtube.com/watch?v=PHe0bXAIuk0  argues that credit is the principal force behind the business cycle.

Is this considered to be a established truth within some school of thought and is there a specific school of thought that disagree?
I think this question is too open-ended and unqualified. One can point to two economists in particular who highlight the importance of debt in the cycle - Hyman Minsky and Steve Keen. Both of these economists are not considered to be “mainstream” (although Minsky has been more heavily cited since the Financial Crisis).

If we look at the data, we see that credit (debt outstanding) grows during the cycle, and this can cause financial distress (not always). However, one could argue that the debt growth is a side effect of growth, and not the causal factor. Even though I am highly sympathetic to Minsky’s work, that criticism appears valid. We need to qualify exactly what we mean, but the question has no such qualifications.