Having done some research I suspect this is Juncus falcatus, sickle-leaf rush. Which is common above 1000m to kosciusko. See, https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Juncus~falcatus https://vicflora.rbg.vic.gov.au/flora/taxon/2f8b0856-eb4e-4eb5-8e30-bc5956dfa9be & page 108, of kosciuosko alpine Flora, by M.gray & C.totterdell.