Background information and summary of my activity:
I started out trying to make a Live USB with persistence for a "Andy's Ham Radio Linux" .iso file (based on Xubuntu 22.04). I tried several of the methods available via mkusb, installing the tools to the 22.04 live-only environment and they all failed to result in an image with persistence (live-only, sans persistence, was the result).
Next I flashed Xubuntu 23.04 to another USB drive, installed the mkusb tools and used mkusb-plug to successfully make an "Andy's" live persistent system. However, many items were not persistent--notably application preferences for the bundled applications and wallpaper selections. (Thunar View >> List View, xfce4-terminal Edit >> Preferences >> Show Unsafe Paste Dialog, and many others, including wallpaper selection.)
Finally, I used the 23.04 environment and tools to create an "official" Xubuntu 23.04 live persistent system, but it suffered from incomplete persistence, just like the Andy's system in trial #2, above.
In my many hours of searching the web, I've found that others have reported similar problems on several websites over the last couple of years or more. Despite my research and own attempts to debug this problem, I still have not found a solution.
Thanks for any assistance,
-Cal