You need 7-Zip (Windows) or a compatible archiver like Keka (macOS).
If the file won't open, it may be partially downloaded or corrupted. Try re-downloading or re-compressing the archive.
Best for archiving, backing up, or sending large files where file size is more important than compression speed. Troubleshooting
For the best reduction in file size, select the 7z format and LZMA2 compression method.
Right-click the space.7z file, select the 7-Zip menu, and choose "Extract Here" or "Extract to [folder name]" . Best Practices for Compression ( space.7z )
A space.7z file is a compressed archive format designed to save storage space by using high-ratio compression methods like . 7z files: How to Properly Open/Extract space.7z
If the recipient cannot open .7z , use .zip instead, as it has native support on most operating systems.