[initself]

I just downloaded El Capitan today from the App Store from the same machine I installed from.

[djrogers]

Yes, releases older than Sierra can still be found if you had previously downloaded them, but Sierra is gone and presumably High Sierra will be as well once it’s been replaced.

[miles]

How to download macOS Sierra

https://support.apple.com/en-us/HT208202

https://itunes.apple.com/us/app/macos-sierra/id1127487414?ls...