The update link for this security update for 10.13.6 only installs Mojave. Anyone else have this problem?

I need to stick with MacOS 10.13.6 for as long as I can as Mojave kills my iMac and I cannot tolerate the new look. I am have vision problems and Mojave just makes my eyes hurt. Anyway, I get notified every day of a security update (HT209193), which proceeds to install Mojave when I select the security update in the app store, much to my surprise. 1) Can anyone tell me how to gain access to the security update for 10.13.16 without installing Mojave, which would defeat my efforts to continue to use my Mac? 2) . Apple Support told me on the phone today that there will no longer be any security updates for High Sierra, as they want you to install Mojave, which renders my iMac nearly useless. Can anyone confirm that they are no longer providing security update support for High Sierra? Many Thanks!