According to the manual (https://www.sonos.com/support/en-us/sonos-user-guide/index.html#t=sonos-user-guide%2Farc%2Fwallmountarc.htm%23TOC_Specifications4bc-1&rhsearch=ARC&rhsyns=%20&rhtocid=_0_2_6_6) the operating temperature for the Arc is 32° F to 104° F (0° C to 40° C).

Quite possibly not. It depends whether there’s any kind of mantel shelf to deflect the rising hot air away from the wall surface. Even so, there could be increased dust in that location.

Over a fire is not a sensible place for expensive, sensitive, digital electronics.

And that’s before considering the unfavourable TV viewing angles, for the panel itself and for the viewer’s neck posture.

I looked at this for another poster, you also need to look carefully at your TV’s temp range. Roasted screens are not a warranty item.

As mentioned a mantle designed to deflect heat might make the location safe.

Been years but I roasted a cherished piece of artwork over my previous home’s gas fireplace when I forgot to turn on the heat distribution fans and let it run in convection mode.