Slop.

Nobody on this website is going to give you a good answer because obviously distaste for the idea of objective reality is not a very materialist position and it's a very esoteric philosophical thing in a way a lot of people here tend to not like, insert Marx quote about changing the world etc etc.

I would try to explain the fundamental premise that's usually behind views like this as someone who is adjacent to a lot of this stuff:

The only reality one can ever describe and accept as real is the one that they are subjectively experiencing. This is true - while others may seem to be experiencing the same reality and indeed there is a lot of real reason to think this (we're communicating, aren't we?) those real reasons, to some, especially those who have conceptions of themselves or experiences that are extremely out of the norm, the idea of a shared objective reality start to feel a bit constructed.

There's definitely a Base that is shared, to use language that may be familiar, but what is often ignored is the Superstructure, so to speak. The beliefs and experiences and emotional associations and internal symbology of each discrete individual and each group of people, in particular cultural blocks.

Imagine, for a moment, that you were born a Medieval Serf. You have no modern scientific knowledge, only folk tradition farming techniques and crafts techniques, and this stuff is going to be freely intermixed with various forms of magic that you and everyone around you takes for granted as something that is real and works. Your beliefs about the nature of reality are going to be a Catholic framework with leftover pagan traditions mixed in - this, again, you take for granted as self evidently true, as true to you as the modern secular materialist view of reality is to us now.

This means that even if we pluck this Serf-you to the modern day, even if you see or do the same things as this Serf version of you in the same context , you are going to interpret them in fundamentally different ways because of these fundamental differences in Superstructure - to an external observer you could appear to experience the same exact thing but your actual internal subjective experiences of reality and understanding of what reality is are going to be completely different, so in a very real way you ARE experiencing different realities.

That's obviously a fanciful scenario but a lot of people with significant dissociation or psychotic symptoms (as the prohibitions on kinphobia, pluralphobia et al suggests is the case with this group - no shade intended for the record I actually love to see that as one of those sorts myself.) it really is like this, I myself personally have had experiences that were genuinely shattering to my sense of reality and ever since my Superstructure has been permanently abnormal and thus my reality is Not the same as the majority of the people I interact with.

But really these fundamental differences do exist between every human - in most cases it's just far far less pronounced, but trauma and brain being wired weird can make the difference really stark, as can comparison to how utterly alien the day to day understandings of reality of past humans could be.

I hope that was a satisfactory explanation of the undergridding of that sort of thought.

It's basically solipsism.

This person is an "anarchist" who think objective reality is an authoritarian conspiracy and advocate for peoples to "create their own reality".

It's chaos magick stuff. It's fine probably if you don't take it too seriously.