...The Julia package manager should install a version of JET compatible with the Julia version you are running. If you want to use JET on unreleased version of Julia where compatibility with JET is yet unknown, clone this git repository and dev it, such that Julia compatibility is ignored.
...In order to run the Petri net editor standalone, install Mill and npm, and then in one terminal in scala/ run mill --watch apps.petri.fullLinkJS and in another terminal in scala/ run npm run dev. The second command should print out a url that you can click on. You may have to run npm install before running npm run dev.