Mac storage basics · Disks, APFS and formats
Does macOS compress files automatically to save space?
Short answer: macOS transparently compresses many of its own files, but there's no Finder option to compress your files or a whole drive that way.
macOS uses built-in file-system compression for many of its own files and some app files, which is one reason Get Info's size and on-disk size can differ. There's no Finder switch to compress your own files or a whole drive this way.
For your own data, the practical options are deleting, archiving to another drive, using more efficient formats (such as HEIC and HEVC), or zipping documents that compress well.