Primarily republicans. That’s the party that benefits most from voter suppression, gerrymandering, shitty voting systems, etc. Ranked choice voting exists in some capacity in over a dozen states, and it trends heavily towards left leaning states.
The more important fact, however, is that it’s an unknown idea that’s not interesting enough to attract attention over more immediate problems.
Bruh dems voted for it. They did what they could with the votes they had at the time. REPUBLICANS stone walled it because it’s party over country for them. They probably hoped that almost getting lynched by an angry fucking mob the sitting president refused to call in the National Guard on would get at least enough to flip to convict, but nope, republicans will apparently literally die before they vote for country over party.