Since High Sierra is too old for my iMac, I cannot figure out how to execute the createinstallmedia command to create a High Sierra boot drive. How can I get a version of createinstallmedia that will work? It used to have a --applicationpath which is what I need.

Ran fine under Mojave and Xcode 10. WIth Catalina beta and Xcode beta (both latest versions although it's always been like this) the whole machine just crawls when Xcode 11 is open (not running) on a simple SwiftUI project. Just now had to open the scanner for my HP printer and it took a good minute before being ready and was again slow when trying to do a scan. Worked ok, but probably 10x slower then under Mojave.I figure there's two possibilities:1) something in my installation is wrong (although Activity Monitor shows nothing unusual). Machine has only 8 GB of ram and it is definitely being mostly used although I only have Xcode and Safari open.2) my iMac is simply overpowered.Neither of these really makes sense. Any ideas/comments?Thanks, Tom