A significant portion of human structures are located close to the coast (seaborne trade having been a huge enabler of economic development for a few hundred years) and are exposed to flooding from rising sea levels, or built in valleys that are increasingly at risk from flooding due to far-above-long-term-historic-norms precipitation runoff (higher atmospheric temps lead to more energy in weather systems; see eg massive floods in Europe in the past few years).
Compared to the other challenges climate change poses those are fairly simple engineering problems. The Netherlands manage fine with large parts of the country below sea level.
You’re ignoring things like the geological conditions in the Netherlands, they have very peaty soil which is fairly impermeable to water. Which makes the task of keep the sea back pretty easy, you just build a big wall.
But if you look in places like Florida, the ground conditions there are substantially more porous. If you try to keep the sea back there with a simple wall, it’ll just flow under the wall through the soil. You would have to dig all the way to bedrock and install some kind of impermeable barrier to prevent most of Florida from flooding due to sea level rise. Something that’s unbelievably cost prohibitive to do.
The Netherlands only exists below sea level because their ground conditions meant it was possible to pump out the country using technology available in the 1740s. If the ground conditions weren’t basically perfect for this kind of geo-engineering, the Netherlands simply wouldn’t exist as it does today.
You’re using an example that exists purely as a result of survivorship bias, as an argument that it’s practical to apply the same techniques or achieve the same outcomes anywhere else. Completely ignoring the fact that your example only exists because a unique set of geologic conditions made it possible, and those conditions are far from universal, and not in anyway correlated with places we humans would like to protect.
The Netherlands has been planning for the impacts of sea-level rise for decades now. At least twenty years ago the government broached the idea (with TV commercials) that they were going to have to abandon some are areas to the sea.
A few critical ingredients being: no denialism about their vulnerability, strong social and economic commitment to reducing vulnerability, lack of reflexively blaming floods on illegal immigrants or trans people
Also they don't blame the climate or weather on democrats there.
and sea level rises are slow enough that countries with more high ground than The Netherlands can just not rebuild/maintain old houses in vulnerable positions and build higher (often just a bit further in) instead.
Some buildings buy the coast (especially in port cities) and have steep rises anyway.
There is a huge threat of cultural loss - e.g. Venice.