The Great Replacement isn't even a conspiracy theory they just built an elaborate strawman that they call it, instead of debunking the original thing lol (because they can't because it can be seen by anyone with eyes)
I've always found it quite curious how Wikipedia describes the "theory":
The
Great Replacement, also known as
replacement theory or
great replacement theory,is a
white nationalist far-right conspiracy theory espoused by French author
Renaud Camus. The original theory states that, with the complicity or cooperation of "replacist" elites, the ethnic French and white European populations at large are being demographically and culturally replaced by non-white peoples—especially
from Muslim-majority countries—through mass migration, demographic growth and a drop in the birth rate of white Europeans. Since then, similar claims have been advanced in other national contexts,
notably in the United States. Mainstream scholars have dismissed these claims of a conspiracy of "replacist" elites as rooted in a misunderstanding of demographic statistics and premised upon an unscientific, racist worldview. According to the
Encyclopædia Britannica, the Great Replacement "has been widely ridiculed for its blatant absurdity."
Despite calling it absurd and untrue in its opening statement, it states something that is undeniable reality in its second sentence.
One of the most fascinating things about this article is that, despite calling the claims absurd and appalling, it provides no evidence
against the theory besides a few scholars saying "nuh-uh". The demographic statistics section, the one where, if the "theory" is untrue, should provide solid evidence that this is
not happening, is laughably short:

Apparently migrant statistics are "exaggerated" and replacement is "unlikely", yet in this very same paragraph it says the amount of muslims jumped from 1% to at least 8.8% in 16 years. In a likely "medium migration" scenario,
this percentage might grow to 17.4%! That particular paper has a truly apocalyptic scenario for Sweden, which in a "high migration" scenario could reach 30% Muslim population. Replacement, at that point, would be an eventuality, even if there was no wider conspiracy, considering low birth rates and aging population among Swedes.
All of this is to say, not much is done to actually try to disprove the "theory" Wikipedia says is so insane. Isn't that interesting? The rest of the Analysis section is a bunch of citations of people calling it racist and numbers on how popular it is. The rest of the article is just talking about its political influence and terrorists inspired by the concept, mostly neutral.
This encapsulates what all of the news articles and videos and such that try to "debunk" this theory are like: it's always calling it racist, appalling, saying it's absurd and that there is no wider plan behind this and not to worry so much about immigration, that more brown people is good actually and diversity is so awesome and rad, and that wypipo were racist colonizers so we shouldn't complain. Never anything substantial or fact-based to counter it, though.
And, even if there is no wider plan, the valid concerns brought up are always completely brushed aside! They never entertain the thought that
maybe there's something wrong with bringing in a ton of people who aren't compatible at all with your country's culture and values, and that many are going to have an extremely negative reaction to the idea of their country increasingly becoming more welcoming of these people than their own populace. I mean, they weren't even consulted on whether or not they wanted something like this, they never got to vote on it, it was just thrust upon them by politicians and now they're just supposed to deal with it?
I'm of the opinion that, while there is indeed a plan to bring in migrants to White countries to replace the aging population, said plan took full advantage of the genuine incompetence of politicans and the bleeding heart of lefties to use as pawns to execute the plan. Nobody actually signing this shit into practice is part of the conspiracy; the conspirators were the ones who generated the idea and spread it. That's what I believe. Now, the thing basically runs itself, without much input from the planners. Maybe it even got a bit too out of hand for them, that's why they're now promoting politicians who want to turn the tide and put a stop to mass immigration!