This is getting deep into the philosophical weeds and I can't really do it justice in an HN comment. I'm happy to pursue this with you in depth if you like but we'll probably need a different venue. But here's my best shot.

> People that meditate do not find this unitary illusion to be fundamental, but find that what seems at first to be a singular entity is in fact an entity consistenting of multiple parts

I don't disagree with this. I've had similar experiences myself, but I see no reason to believe this has anything to do with QM or MW. I think it's just that my conscious self is not all there is of me. I have multiple subconscious sub-systems, but there is only one collection of sub-systems that is me.

> do you think that the mathematical formalism you are endowing with "truth" can even express something like "conscious beings exist" or "a cat is under the table"?

I think it just did :-)

> there's no clear formalism for "person" or "mind" in the mathematics of QFT

I actually think there is, but that's a long story. The TL;DR is that I believe Daniel Dennett got it basically right in "Consciousness Explained", and that decoherence does in fact solve the measurement problem.

You might also find this interesting:

https://blog.rongarret.info/2014/10/parallel-universes-and-a...

It's not completely on point, but it's related.