By the word "idea" in the title I am referring to self-replicating ideas inside minds. You can learn more about them in my post on my neo-Darwinian approach to the mind. Memes are ideas, too, of course—I just haven't found a good name to refer exclusively to self-replicating ideas inside minds yet. (If you have any ideas that rhyme with "gene" or "meme", let me know in the comments below!)

David Kedmey asks:

Yes, that's actually another analogy I had in mind:

Meme replication across minds might be analogous to one person's mind constructing similar ideas from various parts (problem-situations) of the neocortex...each with disparate sensory inputs. Converging on one good explanation.

— David Kedmey (@DKedmey) February 19, 2021

Related Q: how does copying / replicating an idea within a mind work? How does it differ from meme replication across minds?

— David Kedmey (@DKedmey) February 19, 2021

Let's do it step by step:

how does copying / replicating an idea within a mind work?

Through something like a quine, but less reliable so that mutations occur.

How does it differ from meme replication across minds?

It's very different. For one thing, memes exist in two distinct physical forms (see chapter 15 of David Deutsch's The Beginning of Infinity), whereas self-replicating ideas inside a single mind only exist in a single physical form (until they optionally turn into memes). Another difference is that people copy memes creatively, and often (though definitely not always) copy or enact them consciously, whereas idea replication is neither creative (because it underlies creativity) nor conscious: idea replication is completely subconscious and outside our control. It just happens automatically.