They may be referring to the fact that the two parties will often join forces to protect the status quo. Where you see support for things like ranked choice vot

They may be referring to the fact that the two parties will often join forces to protect the status quo. Where you see support for things like ranked choice voting, or easier ballot access for third parties, you see less support from the established party leaders because the status quo is their best case scenario. It's all about democracy as long as you have the majority. While in actual votes the parties may differ, in principle I often fail to see any clear difference in philosophy. Someone running against the incumbent will slam them for abuse of executive orders and support for the Patriot Act. Then they'll get in office and sign a renewal of the Patriot Act and issue more executive orders than their predecessor. In that way I see them as a uniparty on many issues. In other ways Republicans are just anti-Democrats and Democrats are just anti-Republicans. They seem to use the same arguments on different issues depending on what happens to suit them or what politician they're defending. I've seen Republicans slam Biden for his failure in Afghanistan and failing to get Afghan nationals that helped the US military evacuated. But watch them do a 180 as soon as any of those Afghans arrive here. Which party believes you have absolute autonomy over your own medical decisions and that doctors need to treat you according to your own wishes? Well it depends on the treatment we're discussing. It doesn't depend on any consistent principle. Call it a uniparty or not - I just don't trust either to be sincere about any democratic principles anymore.