There are several types of “Saṅghabheda.”
However, saṅghabheda can become an anantariya kamma that will lead to rebirth in an apaya without exception only for a bhikkhu. Furthermore, the version in the first sutta may not be an anantariya kamma, even for a bhikkhu. No one knows the correct Dhamma until heard from a Buddha or a true disciple of the Buddha. I have heard Waharaka Thero explain that in a discourse. If I can find it, I will discuss it here.
– I think the one that qualifies as an anantariya kamma is to do with breaking a Vinaya rule and deliberately splitting the Bhikkhu Sasana. Devadatta did that when he split off and took 500 bhikkhus away. That was one of his anantariya kamma.