ImageInTerminal with Plots integration in a sixel-enabled terminal works in Julia 1.8, not 1.9rc2

I was trying to use ImageInTerminal with Plots in a sixel-enabled terminal (eg, either mlterm or latest Konsole), I was surprised that, when all graphics correctly appeared inside the terminal with Julia 1.8, only image display, not Plots commands, apperaed in terminal with Julia 1.9. it seems that in 1.9 Plots does no longer recognize the Sixel enabled extension.

Reproducer :

using Images,TestImages,ImageInTerminal,Plots
testimage("mandril_color") # shows inside terminal in both 1.8 and 1.9
scatter(rand(10)) # shows inside terminal in 1.8, shows in separate GR windows in 1.9 (so doesnt shows when ssh without X11)

As I understand the difference is the in 1.9, Plots is using the ÌmageInTerminalExt` package extension. What could be the issue ? (and the solution !)