Affordable Care ACT-If a dependent (under age 26) makes an high income, will they still be covered under their?

You can be covered under their plan, but your parents will pay for it. You don't ride for free. But you can't be kicked off the bus if your parents pay the fare.

The ACA only says health insurance companies must allow parents to keep their adult children on their policies until the age of 26, if the parents choose to do so. The child's income or ability to get insurance through their own employer is irrelevant; if the child prefers coverage under the parents' policy, and the parents are willing to cover the child under their policy, the insurance company must allow them to do it.

It is not automatic. Parents must request to add their adult child. The income of the child does not matter when calculating insurance premiums. It does not matter if the person is a tax dependent or not. That has nothing to do with health insurance. The premiums will be higher to add the person.

If you have your own healthcare plan under employer than you don't need ACA.