I downloaded the tar folder and extractred it and ran the .run file. I clicked continue all the way through and accepted and even see the file that downloaded on my desktop and file manager yet it says: We are not able to detect the installed plugin.
I had the same problem when installing on KDE (openSUSE 15.1, chromium). It turned out to be that libappindicator3 was missing. After installing the missing library and reinstalling the plugin everything worked.
To find the problem and fix it I did this (to just fix, goto 4):
uninstall the plugin (run unistall script)
open up a terminal (Konsole) and go to the folder containing the installer for the plugin (most likely at ~/Downloads/ArduinoCreateAgent-1.1-linux-x64-installer-chrome)
Run the install script (./ArduinoCreateAgent-1.1-linux-x64.run ) and read the error messages. Mine read "error while loading shared libraries: libappindicator3.so.1: cannot open shared object file: No such file or directory"
install the missing library. On openSUSE it has its own package in the standard repo.