I've just done my kitchen, with two flooring options. It was a new build kitchen, moved the kitchen to a new space.
Existing flooring I have finished first, but that was sanding and polishing floorboards that I didnt want all that mess in the new kitchen.

New build portion that needed finished flooring, kitchen went in first then flooring to under cabinets, sort of, just enough to be covered by the kicks.

You dont want cabinets sitting on a floating floor, but if you have solid flooring like solid floorboards or tiles, then you would want them under the cabinets.