Plugin. These LibreELEC builds don't include urllib3 - that's a module installed by the add-on system and is the source of the warning. The plugin should be fixed.
Texture Cache Maintenance Utility: Preload your texture cache for optimal UI performance. Remotely manage media libraries. Purge unused artwork to free up space. Find missing media. Configurable QA check to highlight metadata issues. Aid in diagnosis of library and cache related problems.