Trouble downloading installer for thumb-drive OS installation.

I'm trying to create a thumb-drive OS installer for a 2011 iMac. When I click on the link in the article above to download an installer app for macOS High Sierra to my Applications folder (as described above), it does not do this, it opens the App Store and only offers me to "Get" this OS on my computer--which is a 2019 Macbook Pro running Big Sur, which I do not want to replace with High Sierra. How do I access just the installer for High Sierra?