Hi,
in my bedroom i've an old tv and a raspberry pi (pi 1 modela) that i use as a htpc. before i installed libreelec i used an old version of raspbmc. on that system i could "disable" creating thumbs only by change the permissions of the thumbs folder in the home directory to 000 (chmod -R 000). so kodi had no right to write images in that folder. this speeds up the system a little bit- whats important on that very slow hardware.
but this doesn't work with libreelec. i change the permissions but kodi creates still thumbs and i also can create files and folders in the thumbs folder. how i can fix that? it seems there isn't a possibility to disable this in kodi or libreelec settings?