How do I make a new global variable? I would like answers for both 2023.1 and the latest version.

When you are in the workspace, on the left of the add mod element button you have 5 pages. Click on the one called Variables. Click Add new variable. Give it a name and set its variable type to whatever you need. And choose how it saves the value(s) for each instance. Read this article to see what fits you needs the best: https://mcreator.net/wiki/variables.