u/Darn_near70

I was listening to a pop singer in McDonalds background music the other day and found it hard to ignore a less than subtle "change in keys" (a half-step up). It got me wondering, as someone not well-educated in music, how orchestras deal with the kind of real "key changes" that were common before equal temperament came about on pianos, where keys had their own character due to difference in tone intervals.

When orchestras play with a pianist, do they consciously adopt equal temperament? Does this happen in Baroque, Classical, or Romantic music? Or is it a non-issue? Are there some instruments that struggle to play in equal temperament?