Use the Unifi phone app to manage them. You can manage the APs themselves without logging into anything. I’d recommend updating the firmware after 8 years, you can always do a hard reset to get the original back.
Hard reset will not automatically downgrade the firmware.
And I don't think it's a good idea to manage multiple APs using the app instead of from the controller. Managing a single AP from the app is ok, but I think you'll run into problems when you have multiple in a network.
OP didn’t ask about managing from the controller. I prefer the controller and use it myself. Some of my family members do not want a controller and use the Unifi APs I suggest.
For example, you can't set up meshing from the mobile app. Best you can do is give them all the same SSID/password, and they also have to be wired in that scenario.
