Having recently upgraded my Wifi router's firmware to one that supports WPA3, I tried to adjust the corresponding WiFi connection settings on my laptop running 20.04.1 by selecting "WPA3 Personal" on the 'Security' tab (the 'Details' tab shows that WPA3 support is advertised by the router as expected).
Despite deleting and re-creating the connection profile and multiple reboots, my laptop always connects over WPA2 (as reported by the router's UI). A telltale sign is that the drop-down setting on the 'Security' tab flips back to "WPA & WPA2 Personal".
My laptop's hardware supports WPA3; the router had to be setup in mixed mode (WPA2+WPA3) due to some legacy devices that don't yet support WPA3. My iPhone and other iOS devices immediately took advantage of WPA3 after the firmware upgrade.
Other WPA3 questions relate to 18.04; the version of network-manager (1.22.10) shipped with 20.04 ought to support WPA3 out of the box.