You and your source are engaging some distortion/mis-statement.
From your link;
...
Nearly six in ten Marketplace enrollees (57%) live in congressional districts represented by a Republican. Generally, enrollment in ACA Marketplace coverage by congressional district is largest in the South. At least 10% of the population is enrolled in ACA Marketplace plans throughout all congressional districts in Florida, Georgia, Mississippi, and South Carolina, along with almost all in Texas and Utah.
MAP
While a relatively small share of the national population gets their coverage through the ACA Marketplaces, in some districts, the number of ACA enrollees could be enough to swing a close election. ...
...
Since the enhanced premium tax credits became available in 2021, ACA Marketplace enrollment has increased significantly in some red states, and 57% of enrollees now live in Republican congressional districts.
www.kff.org
Looking at the interactive map included in this article, only seven mostly Southern states are mostly the black color that would be 10% +. This doesn't seem to back-up the author's claim about 57%. Would seem the article is trying to imply this 57% figure is a nation wide data but it isn't documented or actually proven in the article.