I reported this keylargo bug in 2016, no solution so far.
An external keyboard is a workaround.
Sounds like this is a confirmed issue.
I will hold off on registering MorphOS on this PowerBook until this is resolved.
This issue smashes my dreams of using CygnusEd while sitting out on the porch. ;)
As an aside -- this is not the first time I've had issues using Apple keyboards on alternative operating systems. Using the "flat" aluminum Apple USB keyboard on my Raspberry Pi (running Raspbian) has also resulted in extra keys entering the input stream, though perhaps not exactly in the same style. It has made me wonder if Apple's keyboards actually have firmware bugs which are addressed by Apple in Apple's own drivers.