ASUS recently had released a beta firmware to the public featuring WPA3 and OFDMA support for the RT-AX88U router. The firmware can be downloaded from ASUS Global website.
Adding further the salt to the wound, you will need a WPA3 client-certified to fully support the feature. You can further join a dedicated thread discussing the beta-firmware here.
Related Review: ASUS RT-AX88U Review
The router can be rolled back to the stock firmware or Asus-Merlin (if you use it) by flashing to the latest stable firmware. However, the process only to be executable via manual firmware upgrade via Web UI only.