Yes, a nice example is to look at a hi-resolution photo of Earth from space. Much of humanity lives along coastlines and rivers, especially where a river meets the sea, as you get ocean access and river access to both global and inland trade, along with fresh water and a convenient way to get rid of waste.
Civilization settled where trade was convenient, with few exceptions. Before flight, water was the best, fastest way to trade. Once we mastered the sea, and were no longer confined to rivers and coastlines, civilization flourished with increasing speed. A few centuries back
According to Harvard University,* in this era: " More than 2 billion people, an estimated 37 percent of the world's population, live within 60 miles of the coast and would be affected, directly or indirectly, by incursions of the sea."
If we increase that to about 93 miles,** then the number jumps to approximately 44 percent.
The Harvard article is talking about a 3 to 5 foot increase in sea levels wiping out much of the coastal infrastructure worldwide, as much of it is built on flood plains frequently no more than 3 feet or so above sea level.
I would think it a safe bet that a 300 foot rise in sea level would affect a great many more, likely much more than 50 percent.
**UN atlas of the oceans: /CDSServlet?status=ND0xODc3JjY9ZW4mMzM9KiYzNz1rb3M~