Is it necessary to secure the secret (e.g., key) in the .so file?

A private key has been #define in the C code of .so file. This key is used for the customized authentication process between client-server.

In some videos, people show how to disassemble .so file using IDA. The output looks like assembly language. How difficult to extract the key value from such output?

If the answer is the key defined in .so also needs protection, do I need to apply obfuscation on the C code before converting it to .so? Whether the normal algorithm will be affected for C?