I have
View > Flip Text Automatically set, and this appears to cause the
Flip Text box in the Gerber export to actually be disabled and ticked automatically for all bottom layers.
Never had any problems with silk screen text coming out wrong on boards. I don't recall ever changing that View menu setting, so I think it's the default.
If you want to actually read the text on your bottom side, you can always do
View > Mirror which will give you the true view of looking at the bottom of a board.
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