For most courses, it’s on the basis of UCAT results (e.g. UQ, Griffith, CQU, Adelaide, Newcastle & UNE, WSU & CSU) or UCAT combined with academic results (e.g. CSU, UNSW, Curtin, Monash).
This means that if you want to have the best chances of getting an interview, your UCAT score needs to be as high as possible. The minimum UCAT threshold for receiving an interview offer changes every year (since it depends on how applicants perform that year), and it’s never released until after the UCAT exam, if it’s released at all.