That's literally a photo of it happening at the only scale that matters. The solution is that once the moon is there, we just need to stop it from moving away.

Problem solved forever.

But more importantly, what color should the curtains be?

A orbiting, remotely positional, moon-sized sun shade? That's crazy enough to work I think you've solved the heatwave here

Couldn’t we do this in a more localized way for large cities? Like a big ol’ shade satellite for areas being dangerously affected by heat waves? I know it’s just a bandaid but we will need these kinds of extreme weather mitigation techniques to keep us alive so we can solve climate change or die trying.

Ps I’m not a scientist, so this is a sci-fi idea only - as in idk the maths of what this would take.

It's not really hard to implement at all but would just trade pest for cholera. We could just burn a lot of coal again, the dustier and dirtier the better. But that's pretty bad for air quality but it would seriously cool the planet.