Good morning.
If it helps, I was able to find out which lube is used on the Fatar keyboards (it seems to me that someone asked for it some time ago, but I don't remember exactly).
It is a low friction silicone grease; Unfortunately, however, sold only for industrial use in large quantities (and at a fairly high cost):
it is the Molykote G-807
It is a silicone grease with an inorganic base (PTFE) and NLGI 1 consistency.
For consumer use there are silicone/PTFE greases with an NLGI consistency of 2 to 3, so it seems almost impossible to find a suitable substitute for commercial use with the same consistency.
But in any case, putting a silicone/PTFE grease is at least guaranteed compatibility with various metals and plastics/rubber (except the contact strip, which is also silicone and therefore must not come into contact with silicone grease, as it will be quickly damaged; no problem instead for the bubble strips of the tracker touch, they are in TPE).

This is the same grease that is also used on Fatar piano keyboards (and is probably also used by other manufacturers such as Yamaha, Kawai, etc.)


Beware that not all PTFE greases are silicone based (and even silicone greases can have thickeners such as lithium soaps, and other additives). It is always necessary to check the technical data sheet to be sure of the composition and compatibility of the materials.