"In November, when voters elect three City Council members from each of four large districts, they will do so with a version of ranked-choice voting not used in any other U.S. city.
Voters will be allowed to choose up to six council candidates in order of preference, and candidates will only need 25% of first-, second- and potentially even third- and fourth-choice votes to win."
It looks like the difference between the RCV elections you linked and the Portland one is that the Portland election has 3 seats available per district race instead of 1. There are at least 3 ways that could be managed:
Do a standard RCV elimination, but stop once you have 3 candidates left.
Do a standard RCV elimination until you have a majority candidate. That candidate gets one of the seats. Then remove that candidate, reassign their votes, and continue elimination until you have a new majority candidate. Repeat.
Do a standard RCV elimination until you have a majority candidate. That candidate gets one of the seats. Then restart the RCV count for the second seat with voters’ 1st choices, but the first seat winner removed from the running. Repeat for the third seat.
Ah. STV isn’t particularly complex to understand, either at voting or calculation time. It’s a decent choice for multi-winner elections, which it sounds like the Portland election is.