So I started thinking about running linux on my older macbook, as there would be times when it would be good to run linux there.
I can run linux on my audio PC, but I have to swap SSD's and its kind of a hassle.
So I found this https://www.linuxuprising.com/2019/08/rufus-creating-persistent-storage-live.html
You need to run rufus on windows, so obviously need access to a windows machine.
This will let you run linux from a usb stick and make changes. The last part is the key.
With a "normal" usb stick running linux, if you try to make a change or install a new program, it's forgotten next time you boot up.
With persistence, its is supposed to remember changes made and programs you install.
So its a little more work, but will make it easier to work with, and try out on a stick without wiping out your macos.
This is really a new feature for rufus, so it appears to only work with the latest ubuntu desktop version 19.10.
There are other ways to add persistence, but rufus looks to be the easiest way to get there.