Once you've downloaded the Mac OS X Yosemite 10.10.5 DMG file, follow these steps to install it on your Mac:
: Your Mac must have at least 2 GB of RAM and 8 GB of available storage . Generally, any Mac that can run Mavericks can run Yosemite.
Potential issues: If the user hasn't downloaded Yosemite before, the App Store might no longer offer it. In that case, they might need to upgrade their Mac to a newer version, or check if there's a way to access older versions via Apple's developer site with an account. Also, verifying the integrity of any download is crucial to avoid malware.
Apple provides direct download links for older macOS versions via their support website. macOS Yosemite 10.10 (Full Installer) : You can download the OS X Yosemite 10.10 DMG directly from Apple's servers. Yosemite 10.10.5 Combo Update