You need 7-Zip (Windows) or a compatible archiver like Keka (macOS).
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 space.7z
If the recipient cannot open .7z , use .zip instead, as it has native support on most operating systems. You need 7-Zip (Windows) or a compatible archiver