How do I get through a work happy hour at 3 weeks sober?

You have three fine options and none require a speech: (1) Skip it — 'family commitment' is a complete sentence, and at 22 days protecting your quit beats office optics. (2) The veteran move if you go: arrive early when it's tame, get a soda with lime IN HAND immediately (a full glass stops all offers), congratulate whoever it's for, leave at the 45-minute mark. (3) Recruit one ally — telling a single trusted coworker 'I'm not drinking these days, help me dodge refills' turns the room from minefield to manageable. Rehearse your exit line in the car. Mine was 'early morning tomorrow.' It was even sometimes true.