I've recently found out about Coleman's version of panprotopsychism or neutral monism, which aims to get rid of all issues related to panpsychism's combination problem. Coleman actually says that the secret is to consider the qualities irreducible, but the subjects that experience them to be reducible.
Now I've also found an objection on this one, which I don't fully understand due to my lack of technical language and also because I'm not native.

Here's the link for the objection: https://link.springer.com/article/10.1007/s10670-020-00256-x#Sec8

From what I understand, Coleman solves the combination problem but faces an emergent issue: how do you get from non-subjects to subject? Is that what the whole point of the objection is or I am totally wrong? Could someone offer me a simple explanation for the objection presented in the link above?

Thank you!