Where to download High Sierra?

I am trying to upgrade from Sierra to High Sierra on my iMac. I do not want to upgrade the system further because I will lose the ability to use some very important software (Adobe CS6 suite) if I do so.

Here is the problem. I go to the Apple page https://support.apple.com/en-us/HT211683

Once there, I click on the link to download High Sierra. I am taken to the App Store. But when I click on the "open" button to get the High Sierra download I get the following message -

I have contacted Apple Support and talked to them about this. They took me through the same steps I just listed and we got the same results. Their only idea is for me to take my computer to a Genius Bar and have them install the OS. While I don't mind doing this if necessary, I also need to upgrade my wife's iMac as well, and avoiding multiple trips to and from the Apple Store (as well as loss of the computer for a day or two) would be preferred if possible.

Before going the Genius Bar route I thought I'd check here first to see if anyone is aware of another way that I can get the High Sierra OS.

Thanks in advance for any help that you can give me!