I'm working in two places, one with windows PC, other with a Linux PC (for various reasons).
I have LittleFS uploader working fine on the Windows PC e.g. download plugin to appropriate folder in ArduinoIDE file structure, F1 to get the tools up, select littleFS - files upload - all good.
However, for the Linux machine I fail at the first hurdle e.g. I use the 2.3.6 ArduinoIDE AppImage - no problem. But - I can't work out where to put, or how to get the LittleFS plugin to work with the AppImage as there is no file structure due to it not being "installed" in the traditional sense.
So - does anyone know how to get LittleFS working with ArduinoIDE AppImage? Or alternatively how to install 2.3.6 on linux (so that i get the traditional file structure)?
That is completely irrelevant. The AppImage is only a container for the Arduino IDE application. If you follow the correct extension installation procedure, you are storing it in a folder completely separate from the application.
Copy the VSIX file to ~/.arduinoIDE/plugins/ on Mac and Linux
So just put the .vsix file of the extension in that folder, then restart Arduino IDE, and you are all set, even when using the AppImage. If you have any questions or problems while doing that, just let us know and we'll provide further assistance.
Your confusion indicates you might have incorrectly installed the extension inside the Arduino IDE application installation on your Windows machine. The problem with doing that is the extension will be lost each time you update to a new version of Arduino IDE. So you might want to also review your Windows installation to make sure you installed the extension correctly:
As I explained, this is not necessary. However, if you do want to do that just select the "Linux ZIP file (64-bit X86-64)" option from the menu on the "Software" page:
Note that we recommend the AppImage due to the fact that it supports the auto-update feature. When using the Linux ZIP package you must update to new versions of Arduino IDE manually by downloading the new version from the "Software" page and then replacing your existing copy of the IDE with the new version from the downloaded ZIP file.
Thanks, I have now found where is should live. For those not fully familiar with the Linux file system (including me) the plugins should live here:- "/home/[user]/Arduino/.arduinoIDE/plugins". at least that's where it is on my Linux Mint installation.
It should instead be /home/[user]/.arduinoIDE/plugins (note the .arduinoIDE is directly under the user home folder, not under the Arduino subfolder). The ~ used in the extension's installation instructions is an alias for /home/[user].
/home/[user]/Arduino is the default location of the Arduino sketchbook folder. The sketchbook folder is where Arduino IDE Library Manager installs libraries, and is also a convenient place to store your sketches. However, it is not used as a place for installing extensions.
The only possible reason for the extension installation folder being at /home/[user]/Arduino/.arduinoIDE/plugins would be if you are using a modified version of Arduino IDE instead of the official version downloaded from the "Software" page of the arduino.cc website.