A good way to see that instant runoff voting is nonpartisan is to look at examples both of when it could have helped a Republican and when it did help a Democrat.
In a 2018 Texas House race the Libertarian candidate got 1,106 votes, most of which likely would have ranked the Republican as their second choice and enabled Republican Mike Schofield to win. However, he lost by just 113 votes to Democrat Gina Calanni. This could have been an RCV win for the Republicans.
You can see the opposite result where RCV was actually used was in Maine’s Congressional District 2 in 2018. Republican Bruce Poliquin won the plurality vote. However, when votes received by the two candidates who received the fewest votes were reallocated based on RCV, the winner was Democrat Jared Golden. Hence an RCV for the Democrats. RCV is truly a nonpartisan change in voting logistics that enables election of the candidate with broader support.