This thread discusses how to force the date: Some downloads may error out because of date. Please note: Night Shift, and two factor authentication needed to unlock AppleID accounts did not come about until 10.12.4 on Mac OS.

offers instructions to get the download link for El Capitan installs on top of older operating systems.

Additionally the certificates may make a download appear not available. Note, some downloads from Apple do not work in Safari for earlier Mac OSes, see this tip if you find you can't download them anymore, to find a browser that will work. Download based on manual time may fail, especially on older systems where the system time is not set right. Go to Apple menu -> System Preferences -> Date and Time and select the closest time server to set your time, and do so. All other Mac series have an OS of Yosemite or older which can be upgraded to Monterey.

The MacBook without the Pro or Air moniker with the Machine ID of 9.1 from early 2016, and the iMac Late 2015 with the Machine ID of 16,1 are the oldest Macs that can upgrade Monterey that shipped with El Capitan. If it is not running 10.12 yet, but was prebundled with 10.11, it can be upgraded to 10.12 first, then upgraded to Catalina. If a Mac shipped new with 10.11 it can be updated to 10.14 Mojave direct from the Mac App Store.

Docker on mac 10.6.8