Can’t install older macOS to partition on my new MacBook Pro 16”

I am trying to install an older version of macOS to my new 2019 MacBook Pro 16”, but I am running into problems doing so. I want to add it as a separate bootable partition because there are a few 32-bit programs I need to use from time to time, and Catalina obviously won’t work for that. I’m trying to install High Sierra, but I’m getting stuck at the install point with a circle-with-a-slash / “prohibited” symbol.

Here’s what I’ve done so far:

• downloaded High Sierra installer from apple (I’ve made sure it’s the full version; I know there is a smaller version that has to download the rest.)
• made a bootable USB using DiskMaker
• made a separate partition of enough size for High Sierra and the extra stuff I plan to install
• attempted to boot from the USB holding the option key

At this point the disk appears with the High Sierra installer logo and name, but when I select it to boot from, I just get a black screen with the “prohibited” symbol.

I’ve tried several USB drives, several different USB-C adapters, remade the drive a couple of times, and no luck. Could this be due to using an adapter for the drive? Or is my MacBook just too new to allow one of these older operating systems? In the worst case I can probably get away with using Parallels, but if possible I’d like to be able to boot into the second OS.

Any thoughts much appreciated.