Or quit at the end of the year.
I FIREd in Dec 2019, which meant my employer healthcare ran through the end of the year, and I could have a full year of anticipated low income for ACA subsidies. This worked pretty well for me.
I applied during open enrollment (though I qualified for a special enrollment period as well) in Nov 2019 for 2020 ACA coverage - my state uses the national marketplace. My 2019 income was about $110k, and $100k or so on my 2018 taxes (single). When I stated my anticipated 2020 income would be $16k, the form asked why the difference, and I was able to select "job change/loss" and it accepted it - no further questions and no proof required. Your state might be different, but it was incredibly easy in mine.
When I re-enrolled last Nov for continued 2021 coverage, it still accepted my estimated low income, even though I still have not filed a tax return (FWIW, I hit my target $16k income almost right on through Roth conversions).
I don't anticipate being able to get max subsidies forever, but it's nice to take advantage while I can.