I followed the guide above using LuCi, stopping at:
" The remote wireless station
...
Go to Physical Settings and enable STP. Failing to do so can allow a network loop to form that will take down all routers."
At that point, I have the following active Wireless networks all appearing to be working fine:
SSID: 2.4g | Mode: Master
BSSID: 00:xx:xx:xx:xx:AC | Encryption: mixed WPA2/WPA3 PSK, SAE (CCMP)
SSID: 5g | Mode: Master
BSSID: 00:xx:xx:xx:xx:AD | Encryption: mixed WPA2/WPA3 PSK, SAE (CCMP)
SSID: 5g | Mode: Client
BSSID: C3:xx:xx:xx:xx:DF | Encryption: WPA3 SAE (CCMP)
Then I read the next paragraph:
"Finally, add a new wifi network if you want to join the network via wifi. It can have the same name, password and settings than the WDS access point, or they can be different. When creating the new wifi network, under General Setup, ensure that Mode is Access Point and Network is set to Lan."
Since I already got the two Master-mode Wireless networks up, I don't think I need to add any new one. However, this paragraph did make me do the opposite, disabling both of them, just to be sure, since my most important goal is to get the WDS bridge working.
The Client-mode WDS bridge does keep on working with the two Master-mode ones shut down, while I'm connecting to it via wired Ethernet.
Then, I figure I do like to be able to connect to the WDS Client via Wifi too. So I proceed to turn on the Master-mode 2.4GHz SSID. No problem. But, when I turn on the Master-mode 5GHz SSID, the Client-mode 5GHz SSID for the WDS bridge drops off. While it's not that big of a deal (keeping the Master-mode 5GHz SSID down), I am curious if this is expected behavior. And even if the Master-mode 5GHz is supposed to be able to remain on along aside the Client-mode 5GHz SSID for the WDS, is it considered "best practice" to shut it down anyway?