The observed behavior on my Pixel is that it generates a new, random MAC whenever you connect to a new network. It reuses that MAC for that network going forward. It does not ever use the "real" MAC unless you specifically select that in the settings.
> In Android 10, MAC randomization is enabled by default for client mode, SoftAp, and Wi-Fi Direct.
It randomizes per-SSID, so you get a random MAC per SSID you remember on your phone, this ensures privacy while not breaking DHCP / static IP etc.