Resolved: There was an error downloading the plugin list.
I decided to try once again to use the plugin manager to get the TextFX Characters plugin.
Ran Plugin Manager... it needed to be updated.
After the update:
- It has ads: "Plugin list hosting generously provided by" (some business I'd like to DDOS)
There was an error downloading the plugin list. Please check your internet connection, and your proxy settings in Internet Explorer, Edge or Chrome.
So we went backwards.
I changed the setting that says "Force HTTP instead of HTTPS for downloading Plugin List". Restarted Notepad++ and was then able to download the plugin list and install the TextFX Characters plugin.