On Android 11, there is a new option "Wi-Fi-enhanced MAC randomization" in the developer options.
When you enable it, delete/forget the network, and then reconnect, you get a new MAC address every time. Also, you get a new MAC address for this WiFi/SSID when you reboot your device. Disabling and enabling WiFi is not enough to get a new MAC. With this enabled, the device also generates a new random MAC address every few days.
When you disable this option, you get back your previously used random MAC.
Please also read liangpig1's answer, which is very informative.