Hawkgirl’s last appearance was in Justice League #39 (March 2020). As you remember last time the Scott Snyder run came to a completion as the Justice/Doom War came to an abrupt and somewhat unsatisfactory end. With that, Hawkgirl (and Martian ManHunter) seem to have just disappeared. However, she does make an appearance in the just out October 2020 issue #51 of Justice League (2018- ), but alas it is only a flashback where she is seen along with other JL team members trying take down Darkseid.
Justice League #51 (October 2020) begins a three-part story arc written by Jeff Loveness and drawn by Robson Rocha