Where did you find the Highlight Fix LMT as a .cube? It’s possible it’s been shared in that form but I honestly cannot recall. The bigger question is where are you applying it? The color spaces in Resolve ACES mode are very unclear, so it’s very possible that you are not applying the LMT in a place for which it was designed to work properly.
(Of course, it’s also possible that this is just a color that isn’t “corrected” by the matrix fix, but I believe it should help with most nuclear blues regardless of camera.)
Have you tried using this DCTL applied via the contextual menu per clip? (only applicable if using Studio version…)