It is there in Gimp 2.10.36 Windows. Just go to File -> Export, add the .jxl filename suffix (somename.jxl) and export.
...but... there is no dialogue for setting parameters see: https://gitlab.gnome.org/GNOME/gimp/-/issues/9936
Closed in typical Gimp dev mode
In linux Gimp 2.10.36 (from PPA) the jxl export does have the settings dialgue.
...but... there is no dialogue for setting parameters see: https://gitlab.gnome.org/GNOME/gimp/-/issues/9936
Closed in typical Gimp dev mode
In linux Gimp 2.10.36 (from PPA) the jxl export does have the settings dialgue.