Never really bought the landing strip idea if im honest. The lines are visible from a few hundred metres up but if you're piloting a spacecraft that crossed the galaxy I think you can manage without runway markings scratched in the desert.
What gets me though is the sheer scale of it. Someone put a massive amount of effort into designs they couldnt even see properly from the ground. That part is genuinely odd and deserves a proper explanation beyond "ancient art project."
The religious/astronomical theories seem more grounded to me but I wouldnt say the alien angle is completely dead, just that it keeps getting used as a lazy catch-all whenever we cant explain something. Interested what others think - is there any newer research that actually moves the needle on this?