Pantheon: Uses the world's largest individual piece of unreinforced concrete as a roof
Parthenon: Almost every aspect of it is curved to make it seem like everything is straight
Conspiracy nuts: Yeah that seems like something ancient people could figure out
Pyramids of Giza: One of the most basic three dimensional shapes made out of blocks that weigh 2-3 tons which could be moved in a plethora of ways as OP mentioned and is actually easier to construct than a cube of the same size because the structure lends itself to a built in ramp set up
Conspiracy nuts: It has to be aliens because the math is too hard!
* Side note: These examples were picked out because they're ones OP used. I realized that the way this is written could come off as a "Yeah, European architecture was more complex than Egyptian architecture" which is absolutely not my intention here. I just don't know how phrase it in a way that makes it clear I'm only trying to emphasize Conspiracy Nut Hypocrisy/racism.
That being said these specific constructions aren't really comparable to begin with.
First of all the Pyramids were made in a completely different time period. I'm talking ~2500 BCE vs ~450 BCE vs ~120 CE. Literally 2,000 year difference here, we are literally closer to the construction of the Pantheon than the construction of the Parthenon was to the construction of the Pyramids of Giza.
Second is they were built with different goals in mind. The Pyramids weren't meant to be fancy complex pieces of engineering. They were built to be impressive and stay impressive forever, which they did a really good job of considering that the impressive version we see today is literally stripped down. The Pyramids of Giza used to be taller with solid white facades capped in gold, the top layer was removed so it could be recycled into different building projects. Meanwhile the Pantheon and Parthenon were built to be impressive in a more pompous kind of way. A "look at our pretty and complex stuff you can't afford to make and are probably too stupid to properly appreciate anyway" kind of statement. Athens was insufferably pretentious about that kind of thing. If I remember right the Parthenon actually set off some conflict within the Delian League because because Athens used the defense funds it collected from the other city-states for what is essentially a vanity project dedicated to a single city's goddess.
If you want to look at Ancient Egyptian structures that have similar architectural complexity you'd want to look at stuff like the Ramesseum or The Valley of Kings. They're both still from completely different time periods compared to the Pyramids and well known Greco-Roman ruins(~1200BCE and ~1600BCE), but they're structures with more frequent use cases than "one guy's burial site". Well, the Valley of Kings is also a burial site, but it was for multiple people over the span of ~500 years so it was more actively maintained than something like the Pyramids. Ancient Egypt is its own branch of study because it just spans such a long space of time and between burying a lot of stuff themselves, constant looting (Worst modern offenders were the British, but they placed so many of their resources into burials that tomb raiding kind of propped up their economy by putting valuables back into circulation. The abundance of concern about tombs being disturbed, despite being a massive taboo to do so, was because it happened regularly), and tearing down older structures for their materials in order to make new structures there's so much to keep track of.
Which makes it even more insulting that instead of bothering to learn anything about this massive and complex culture racists on the internet try to argue that people stacking big bricks in a pile is not only unimaginable but also the most impressive thing they did.