Humanity should be fine. The problem is how to deal with millions of displaced people. We will probably need a few wars to figure that one out.

Yes.

But not while maintaining anything like current first-world culture. You either need to reduce energy consumption significantly or reduce population significantly.

Two guesses how that plays out.

We do it currently. Holland is a good example of fighting back the sea, but at great expense. And not every country will be able to do this type of engineering.

The temp rises are another thing that we can adapt to. Maybe even some global engineering to thwart it. But again it will be at great cost. And this will probably have the bigger impact on all of us. Our eco-system is very susceptible to small temp changes.

The first problem is what you do with the billion displaced people. That’s not a tech problem, so much as an ethical / pragmatic problem.

Yes already now, certainly in 2100.