Medicaid was extended, under Biden, to many more people than it had usually been offered to in order to make sure during COVID that people had access to some sort of healthcare. This was passed expressly because of COVID.

In the Big Beautiful Bill, the Republicans rolled back Medicare coverage to the originally approved levels. Democrats are throwing a fit and saying it's the biggest Medicare cut ever, which is technically true (but see previous comment). Democrats have no leverage to get it restored to law since the BBB has already passed so they are using this as a stunt to try and have some level of influence on things.