for the benefit of the general public - here is the related topic @ LibRaw forum = https://www.libraw.org/node/2552
The issue clearly is that Affinity developers do not Sigma users any option to treat X3F images as monochrome one (= just sum 3 raw channels channels into 1 mono value, instead of converting them into RGB triplet) when they (users) wish... as X3F files do not require any demosaicking that "...and according to `LibRAW`, your images are colour images. ..." is Affinity's non desire to look one iota further into the matter...
