A few seconds after starting the engine on a very hot day, got a red warning message “Generator Fault”.

Car drove fine otherwise, but voltage gauge in the dashboard was reading between 10.9 - 11.4 volts the whole time.

is this indicative of an alternator failure? Any other theories?

 

Yes, that's a bad alternator or something amiss in the charging system
.

 

Update on this…drove it again later today… warning lights never came on, voltage steadily climbed from 11 to 14.2 and stayed there, even with Max AC turned on.

I’m not going to hold my breath that it fixed itself, guess we’ll see what happens

 

very well could have been temperature related. the first week I had my car we had a heatwave, did a quick restart after shutting it off and got a check engine light - freaked me out.
got a code reader and determined it wasn't supper critical, cleared it and have never seen it since (3+ years)

get a ODBC tool and read the codes - will help you in the long run and give you a clue as to what really happened

 

Since we aren't driving much due to COVID I've been charging the battery with an external charger. The Porsche doesn't seem interested in keeping the battery full, and so 12.3 V is usually what I see upon starting until it decides it's drained it enough. I wouldn't be surprised if your alternator is on it's way out....