github[.]com/IridiumIO/CompactGUI
learn.microsoft[.]com/en-us/windows-server/administration/windows-commands/compact
store.steampowered[.]com/app/4339880/Game_Compressor/
Compact.exe is Windows builtin tool to compress files and folders, Not in a packaged file like Zip or 7Zip, but individually on disk. Those files are automatically uncompressed on-the-fly when Windows or whatever app accesses them. How much space is saved depends on the type of file along with the file itself. The overhead to uncompress the files before use is minimal, and some games are reported to actually show an increase in performance because it takes less time to read smaller files. Years ago, when Microsoft was promoting cheaper tablets with low storage, using the compact OS option was popular, but not so much since then. But today it seems there's a revival for gaming, given the rapid increase of hard drive/SSD prices. I thought it might help with drive image backup sizes, but so far it doesn't appear to make the expected difference.
CompactGUI is what the name says, a GUI to make using Compact Much easier. It lets you choose the compression algorithm and shows you the expected new size of a folder alongside the original, so you can see if it's worth it. There are 2 versions, one with .NET 9 & one without. The version without does not seem to work with .NET 10 (?). A folder is added to the Users Local folder where settings are stored, a shortcut is added to the Start Menu, and there's an option to add it to the right click context menu in Explorer. I found CompactGUI via an article on Tom's Hardware where the author recommended the app linked above on Steam, but that one's not free.