Run exiftool Theseus.rar to see if the creator left hints in the comments or creation timestamps.
A differentiable nonlinear optimization library by Meta AI. Theseus.rar
Use the file command to confirm it is actually a RAR archive and not a renamed file. Run exiftool Theseus
If this is not related to a CTF, "Theseus" frequently appears in these technical contexts: Theseus.rar
Check for "trailing data" or files hidden within the archive structure using binwalk -e Theseus.rar .