I read and agree with most but we still can play devil´s advocate only for the joy of it and say in favour of Solipsism, that it may be the case that, we all, are one ENTITY, given as Functions in it, we relate to it all directly or indirectly... So to say, that I am a part in the Whole which relates with the Whole, might be possibly understood as a vectorial expression of the Whole itself in me, or that I am the Whole itself speaking through me...
Yeah, but that would still seem more along the line of a conventional macrocosmic-scale universe that existed even when not observed, than the superficial microcosm of the solipsist -- where only the lawful regularities of the solipsist's "dream" lead to the inference of a huge realm existing beyond the immediate boundaries of the experience (and an incorrect inference if solipsism was indeed the case). That is, the former and grander "world-mind", "nomological system", or "integrated single entity" seems to surpass any categorization of "solipsism", especially if it has multiple agents generating varied personal POVs and simulations within it (or just carrying-out individual agendas if they're either p-zombie agents or purely mechanistic processes devoid of internal manifestations).
The "Public" is it "in", or is it "out" ? does that thing of in or out even makes sense, or is just more concepts ?
Indeed the fuel of solipsism: The external part of experience is just that -- as much a part of a particular brain's experience as its personal thoughts, no matter how much advocates of direct or commonsense perception might wail about mediating processes needing to be eliminated not only in the body but apparently those mediators between the observed and observer in the environment, (light waves, acoustic waves, wafting molecules [odor], etc.)
But if it's to be explained how schizoid Jane's hallucination of "reptilian aliens surrounding her" lacks the same appearance when the corresponding neural or electrochemical patterns in her head are scanned, then an internal or private dimension might have to posited for the externalized appearance, or for the physical properties constituting those patterns of activity. Either that or dodge explanation with eliminativism, phenomenal nihilism, etc.
In a vein similar to the broader definition of neutral monism (post-empiricist brands), I'd speculate that both public/private appearances (matter/mental) are actually the product of a more fundamental order. But such idle speculations often remain untestable.