Heat tolerance

My advice - don't.

Environmental specs for indoor Orbi units appear to be 32F to 104F.  The external RBS50Y has specs of -4F to 122F.

1. I doubt that a typical attic will top out at 117F unless the house is in a really "temperate climate".  In the summer, attic temperatures soar much higher than that.
2. How will electrical power get into the attic?
3. At least 50% of the antenna coverage will be "outside", i.e. not directed toward likely users.

There is probably a specific need that led to this question?

Heat will degrade any electronics over time. Higher heat temps will degrade that much faster. Attic is not recommended for any electronics unless there built for that kind of heat. Would be no reason to place in a attic unless your providing wifi for someone near the roof or sky users.