Does anyone know if the December Lightroom update has addressed the Fuji X-T3 colour cast issue?
If you are referring to the strong color casts when using certain white balance presets, and the odd Tint values shown even under the "As Shot" WB, yes it is fixed. It looks like it was an error in some of the X-T3 profiles.
Unfortunately if you use the "Adobe Standard" profile or the adobe-supplied Fuji camera profiles you will need to reset each image using those profiles to the "v2" version of the profile. See attached screenshot.
Don't forget to make the v2 profile part of your default develop settings as well.