LS50W do not use RAAT so are not Roon Ready due to hardware limitations in the LS50W. This means they cannot be grouped. I use a RPi running Ropieee to feed my LS50W and then use it to “group” that zone.
Also see here:
“Also, note that due to the technical details of KEF streaming these speakers are not Roon Ready, so linking multiple pairs of LS50w is not possible and some RAAT-specific functionality (like convenience switching or advanced Signal Path functionality) is not possible.”