I am using kubuntu 18.04 and Gimp 2.10.12 here so a few more colour management options.
Using the lenna.png standard sRGB image and changing the profile to PhotoGamutRGB icc, exporting that as a jpeg.
Comparing images in a web browser (slimjet - chromium based) the jpeg is very-very slightly brighter than the png. So a colour profile might have a difference, but if both are the same sRGB ???
Both compare the same in Imagemagick. Both look the same in Gimp but then this notebook computer display is not colour profiled. All by eye and subjective. Viewing in XnViewMP - no difference that I can see.
It might just be your colour profiled monitor
Using the lenna.png standard sRGB image and changing the profile to PhotoGamutRGB icc, exporting that as a jpeg.
Comparing images in a web browser (slimjet - chromium based) the jpeg is very-very slightly brighter than the png. So a colour profile might have a difference, but if both are the same sRGB ???
Both compare the same in Imagemagick. Both look the same in Gimp but then this notebook computer display is not colour profiled. All by eye and subjective. Viewing in XnViewMP - no difference that I can see.
It might just be your colour profiled monitor