You're trying to bootstrap objective meaning and morality and something like truth out of nothing using a mishmash of tired ideas from various rationalist or adjacent schools of thought like Kant, Aristotle, Rawls, Plato, etc, while dismissing the schools of thought you disagree with (e.g. postmodernism) using tired cliches.

I'm happy for you if this framework you've constructed works for you, in fending off the derealization and depersonalization you speak about. I've had many of the same struggles, and for a few years actually spent time doing precisely what you've been doing — trying to bootstrap an entire rigid philosophical framework out of nothing using phenomenology and ontology and concepts from across philosophy, building a huge ediface with its own healthy helpings of people like Kant and Rawls. But for myself, as I became more familiar with Stirner, Nietzsche, Novatore, Daoism, post structuralism, and Wittgenstein, I found a better way for myself, where I wouldn't have to forever keep fighting an ultimately self-deluding battle defending a framework built on the rickety foundations of rationalism and, ultimately, nothing at all.

I've realized that my inclination to do so was born out of a few fundamentally false assumptions left over from the death of religion in our society, which I had unknowingly bought into, and which were desperately reaching out to trying to reestablish a religion around themselves because it's in their naturetod do so, in the process using me, becoming my masters. But I also realized that, iltimately, it was I who was choosing to listen to these ideas and give them power, so I could just stop.

I think there's a better (and more intellectually clearsighted) answer instead of "reconatructing" the very same ediface that's been crumbling for the last century or so.

How about instead realizing that there's nothing inherently absurd or unlivable about living without objective meaning, morality, or truth, because there never were such things in the first place, just ideas that you gave power. Learning how to immerse yourself in the fluidity of self and existence and finding joy within it? Instead of "taking yourself captive," learning to listen to yourself and your deeply-felt needs and desires, as they emerge from the creative nothing at the center of your being, and enacting them, so that action feels as inevitable and necessary as no action at all? Learning how to see that meaning is just a stance towards a thing or idea, and therefore that you can grant things meaning as pleases you, because ultimately you give meaning to things anyway, so why not own that? Become a conscious egoist, it's fun! We have cookies and hugs at least