Uh, glass is most definitely a solid at all atmospheric conditions where humans reside, including very hot climates.
Lead, on the other hand, is malleable even at room temperature. I believe what you’re thinking of when you say “old church windows” is the fact that the lead soldering holding up stained glass windows does, indeed, start to soften in warm conditions, thus causing the entire window (which is really a mosaic held together by lead) to sag. It’s 100% the lead that’s the problem, not the glass!
BTW, those church windows don’t have to be “ancient” to have their lead start softening. Even a hundred years is enough.
Meanwhile, ancient Egyptian faience (a type of very delicate glass) is holding up just fine thank you very much after four thousand years in the hot desert.
