The top-two system has existed in Washington state starting in 2008, and in California since 2011. In both states, we now have an abundance of evidence that top-two is destructive to minor parties and to voters who want to vote for minor party candidates in the general election.
There have been 186 instances when a minor party member ran for federal or state office under a top-two election in those two states, and there is not one single instance when any of them managed to qualify for the general election ballot, except in races when one of the two major parties didn’t run anyone.
Anyone who knows this, and who is in favor of letting minor parties exist, ought to be persuaded not to support a top-two system. Unfortunately, there are voices who are pro-third party, but who still say they favor top-two systems. One is Andrew Yang; another is journalist and political activist Jared Alper of New York state, who has this Fulcrum article that expresses dismay at how minor parties are treated in the U.S. (especially in debates) but who says he is in favor of “nonpartisan primaries”, which is a synonym for top-two, top-four, and top-five systems. Thanks to Fairvote for the link.