If icy moon craters do not have a central ring of mountains then why not?
The term peak ring was first used to describe the often discontinuous mountainous ring that rises above the floor of large craters on the Moon. Peak rings are internal to the main topographic crater rim. Since they were first identified on the Moon, peak rings have been observed in large terrestrial craters on all large rocky planetary bodies.
Notably, peak rings do not appear to occur on the icy satellites of Jupiter and Saturn, which indicates that crustal rheology plays a role in their formation.
The peak ring is a topographic feature: it protrudes through the impact melt and breccia that line the floor of the crater and stands above the surrounding terrain. As a result, the unequivocal identification of a peak ring in Earth’s largest craters is compromised by inevitable erosion and/or tectonism.
Chicxulub: drilling the K-Pg impact crater (link to PDF)
Or is the 'no peak ring mountains' on water ice moons just old information and now not correct?
The western part of the leading hemisphere of Tethys is dominated by a large impact crater called Odysseus, whose 450 km diameter is nearly 2/5 of that of Tethys itself. The crater is now quite flat or more precisely, its floor conforms to Tethys's spherical shape. This is most likely due to the viscous relaxation of the Tethyan icy crust over geologic time. Nevertheless the rim crest of Odysseus is elevated by approximately 5 km above the mean satellite radius. The central complex of Odysseus features a central pit 2–4 km deep surrounded by massifs elevated by 6–9 km above the crater floor, which itself is about 3 km below the average radius.
Geology - Tethys | Wikipedia
If craters or most craters are formed by electrical processes what happens for frozen water moons?