There are several types of “Saṅghabheda.”
“Saṅghabheda Sutta (AN 10.37)”
“Saṅghabhedakasutta Sutta (AN 4.243)”
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.