Hot take: Almost all programs are actually multithreaded. The only exception is tiny UNIX-like shell utilities that are meant to run in parallel with other processes, and toy programs.
The third exception is programs that should be multithreaded but aren't because they are written in languages where adding more threads is disproportionately hard (C, C++) or impossible (Python, Ruby, etc.).
The third exception is programs that should be multithreaded but aren't because they are written in languages where adding more threads is disproportionately hard (C, C++) or impossible (Python, Ruby, etc.).