ACA subsidy eligibility may be annual, but Medicaid eligibility is based on current monthly income, and if you have a change that makes you ineligible, you lose it. You can’t just decide to “take Medicaid for a year” because you aren’t subsidy-eligible based on prior-year income.
That said, in my secondhand experience across multiple states I won't name, the medicaid office probably won't actually find out or do anything before 12 months are up.
Also, a few states are starting to officially enact "continuous eligibility" and intentionally not check your income for 12 months -- mostly for children[1] right now, but some states for adults[2] too.
[1] https://www.medicaid.gov/medicaid/enrollment-strategies/cont...
[2] https://www.commonwealthfund.org/publications/issue-briefs/2...
Medicaid can actually be very good quality healthcare, if you're located say, near a very good research hospital in a city with a structural oversupply of medical care due to having a lot of med schools.
I'd rather have medicaid living next to a high quality (non profit) health system, than "nice" insurance living in a shithole. All the insurance in the world can't materialize doctors that aren't there