My report back here as promised.

I arrived at the airport even earlier than expected, and went to the gate agent to try and get myself added to the standby list of the earliest flight. She said the flight's full but I could hang around in case someone drops out. I was also confused when she said this cos there was clearly a list of people on standby on the board, and eventually just one person was confirmed.

I waited around for the actual flight I had added myself to the standby list for via the United app during check-in. I was first in the standby list despite being Basic Economy, and there were 4 people in total on the standby list.

A few people approached the gate agent to see if there are any available seats, and they were all turned away by saying the flight was full. I was surprised that the gate agent didn't just add them to the standby list.

I can't tell whether the gate agent was just unwilling to add people to the standby list or whether the passengers didn't use the magic words "standby list" to specifically request that from the gate agent. It's my first time doing this so I'm unclear what the standard process is, but it seems like if you're able to add yourself on standby through the United app, that would be the easiest way since it seems that it's really up to the whims of the gate agent.

But anyway, I and two others on the standby list were confirmed! I even got an Economy Plus seat, which was a nice bonus. (Also to be clear, I didn't fly with a checked bag.)