Apple provides official download links for older macOS versions, including OS X Yosemite 10.10
If you are already running an earlier version of Yosemite (like 10.10.1) and just want to update to the final version, you can download the OS X Yosemite 10.10.5 Combo Update from Apple Support. Download OS X Yosemite 10.10.5 Combo Update - Apple Support mac os x yosemite 1010 5 download dmg link
Use the Terminal command createinstallmedia or a third-party tool like BalenaEtcher to "burn" the installer onto the drive. Security and Modern Use Apple provides official download links for older macOS
Terminal Command: Open Terminal and paste the following command exactly: Disconnect your Mac from the internet
