It seems like vtkDataArray::LookupTable has no use anymore in VTK. Is anyone still using this API, or is it ripe for deprecation? Lookup tables are now dealt with at the mapper level.
If you still use this API, please say so in the comments, so we don’t deprecate something that is actually being used, or so we can at least discuss it 
I’ll give it a few months, maybe another release (VTK 9.2) before deprecating this API if nobody jumps against it. This would leave this API available at least until VTK 9.3.