ensure your security software is up to date to protect against such files. If you've already downloaded or opened this file, tell me: What operating system are you using (Windows, macOS)?
Based on a search, "m0m-21U.rar" appears to be a file name often associated with potentially malicious or unwanted software, specifically or a Trojan [Source 1, Source 2]. m0m-21U.rar
Here is what to know about files with this type of naming convention: ensure your security software is up to date