The initial announcement referenced undisclosed health issues as being the reason Gjert was no longer coaching the boys. It was nearly immediately clear that it wasn’t true (same statement referenced Ingrid quitting running, which plainly would have nothing to do with Gjert’s health), and there have been enough opaque comments since then that has made it pretty clear that the father-coach dynamic was harmful to the family moving forward. So Gjert’s still coaching the 3:32 dude (and appears in the recent interview to be quite healthy), and he’s been coaching him since he was 15. But Jakob, Henrik, and Filip are no longer being coached by him. I haven’t seen anything that even suggests that they are on speaking terms.
FWIW: Anyone who has watched Team Ingebrigtsen can tell you that he is beyond overbearing and obnoxious. He demands the spotlight and the credit—see the statements by Ghert that Marius Bakken has provided email exchanges regarding proving that Gjert lied, etc. There were also nasty rumors about specific events that precipitated the split but I honestly don’t put much weight in them and won’t repeat them here. It seems like Gjert got to be too much for his sons in the wake of Jakob’s gold and Team Ingebrigtsen is no more as a result.