Before opening, upload the file to a service like VirusTotal to check for malware.

A file is a compressed archive created with the 7-Zip software. It is similar to a .ZIP or .RAR file but often uses a higher compression ratio, meaning it can make large files much smaller. Common Uses for Generic Names Like "124.7z"

To extract the contents, you will need a compatible tool. You can download the official version of 7-Zip here .

Could you share or what you expect it to contain? This would help me give you more specific information.

Because "124" is a simple numerical name, this file could represent several things depending on where you found it: