Adventurer of the Dawn

You can use the macro below to check your progress on this achievement;
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a = C_ItemUpgrade.GetHighWatermarkForSlot(i); if a < 237 then print(a, n) end end

Achievements for reaching the itemlevel in each slot:

237: Adventurer of the Dawn

250: Veteran of the Dawn

263: Champion of the Dawn

276: Hero of the Dawn

285: Myth of the Dawn

Macros to check their progress:

Spoiler

237: Adventurer of the Dawn
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a=C_ItemUpgrade.GetHighWatermarkForSlot(i);local c=(a>=237)and"\124cff00ff00"or"";print(format("%s%d\124r %s",c,a,n))end

250: Veteran of the Dawn
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a=C_ItemUpgrade.GetHighWatermarkForSlot(i);local c=(a>=250)and"\124cff00ff00"or"";print(format("%s%d\124r %s",c,a,n))end

263: Champion of the Dawn
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a=C_ItemUpgrade.GetHighWatermarkForSlot(i);local c=(a>=263)and"\124cff00ff00"or"";print(format("%s%d\124r %s",c,a,n))end

276: Hero of the Dawn
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a=C_ItemUpgrade.GetHighWatermarkForSlot(i);local c=(a>=276)and"\124cff00ff00"or"";print(format("%s%d\124r %s",c,a,n))end

285: Myth of the Dawn
/run local n=tInvert(Enum.ItemRedundancySlot),a;for i=0,16 do a=C_ItemUpgrade.GetHighWatermarkForSlot(i);local c=(a>=285)and"\124cff00ff00"or"";print(format("%s%d\124r %s",c,a,n))end

Seems like this achievement is not unlocked yet. Got full 237+ gear in all my slots and neither achievement or crest upgrade have been unlocked.

Logged in today and got the achievement. So it is unlocked now.