where do you go to download an ISO for home users

Terminology. Macs run macOS, iPhones run iOS, and iPads now run iPadOS.

Apple does not distribute ISO installers. The installers are applications for the Mac. Your Mac model needs to support the version of macOS you intend to download.

Don't give us the model number as that A1419 spans from Late 2013 through Mid-2017. Instead, be specific…

From the Apple () menu : About This Mac, what is in the parenthesis, for example (21.5-inch Late 2013 iMac) on your product description line of that panel? That information will tell me what the latest version of macOS you can install and from that I can send you a link to get the last version of macOS for that hardware.

You should have an entry in System Preferences : Software Update offering to upgrade to Ventura 13.6.4 on that Mid-2017 iMac. That is the last version of macOS supported on that hardware.

Otherwise, you can download the full macOS Ventura installer (.app) from the Mac App Store via this link using Safari:

How to download and install macOS - Apple Support

and it will land in your /Applications folder.

I recommend that you have a last Time Machine backup prior to upgrading, and you should check for any 32-bit application dependencies with the free Go64 app if running macOS Mojave (10.14.6) or older on the iMac — because Ventura only supports 64-bit applications. That eliminates any Microsoft 365 or Office for Mac Suite older than 2021, Apple's Pages '09, iMovie '09, and Aperture. It may also require new printer/scanner drivers so check for macOS 11 support before any upgrade to Ventura.

iOS is the operating for iPhones. Are you looking for macOS? First you need to see which is the latest version compatible with your iMac, see below.

https://www.macworld.com/article/673697/what-version-of-macos-can-my-mac-run.html