I got curious, so i dig Bitcoin Core repository and found out both REST and RPC use same port[1]. It implies Bitcoin Core can't use both at same time.
This is incorrect, you can use both RPC and REST at the same time.
For example:
--snip--
Thank you for the correction. I just tried that on my Bitcoin Core node and indeed both RPC and REST works. Although i find it's very unusual one port accept two different protocol since most software usually would separate it.