Ottawa, Canada wasn't purpose-built but was an insignificant city meant to be a neutral choice of capital between Anglo and Francophone Canada. This has also worked fine.

Byzantium was a city for centuries before Constantine was born, and a fine place to control the grain trade from the Black Sea.

There was a city there but it wasn't that large and was dramatically redeveloped after it became the new capital:

https://www.thegreatcoursesdaily.com/making-constantinople/

Not to mention being closer to the Silk Road trade routes through Asia.

Interesting list

Both the Canadian and American cases are not a relocation that made it too far from the original place

Constantinople was a major port way before Byzantine times. Calling it a purpose built capital is a joke. It was a purpose-assigned capital though.