O'Zapft is

Munich Oktoberfest starting hammer phrase. Without these words, the Oktoberfest taking place this year from Saturday 17th September until Monday 3rd October, cannot start.

Normally it ends on the first Sunday in October, but this year, Germany's National Holiday is on Monday 3rd, so it is extended by a day.
Posting in retrospect, I can add this:
Here is a link to 2.5 hour long Bavarian TV programme covering the opening of the 2022 Oktoberfest & at 1hr: 0 min: 0sec the actual act of opening. when the phrase is used. Although in German/Bavarian, the scenes might be interesting for those who have never visited the Oktoberfest as it shows lots of the things that go on in front & behind the scenes. It's a lot more than 7 million drunks!

Today was collecting some horse bedding at the agricultural supplies market. This not very cheap offer of 5 bottles of beer & 2, 1 litre glass mugs (Mass), didn't get me to buy it but caught my eye.