I also think you should normalize for yourself and your workplace that there are times when you are not there. If only you can answer a question then there needs to be better documentation. See it as a trail run for when you get hit by a bus. If they will struggle without you then that is a problem that needs to be fixed. If you are always reachable these problems will never surface.
IMO this is not a universal truth - I’m sure some people need that level of disconnection, but I don't find I'm one of them. I generally like my job, and don't find that forcing myself to disconnect does me any particular mental good. But other people report needing that separation, and that's fine! I don't think there needs to be a one-size-fits-all answer here.
I do agree with your bus factor argument though.
I think we believe ourselves to be more irreplaceable than we are. And if you really think you are irreplaceable then the problem is not going on vacation but being irreplaceable. Because then if something were to happen to you they are screwed.