If global human CO2 emissions stopped, the ocean would be absorbing some of the current atmospherical CO2, so it would start going down.

The ocean is already currently absorbing, and acidifying as a result. It is not currently in equilibrium. Of course, as it warms, its ability to absorb lessens. Warm water holds less CO2, used as a denialist talking point to say that the CO2 is from the oceans, not from humans. But it actually makes the problem worse.

But what's even more important about the nature of this problem that local emissions don't matter. If the US stopped but EU and China etc continued, the US heat dome problem would still go on. That's why this needs to be coordinated internationally. It really matters a lot what the US president and congress does regarding international treaties.