Data collection by the extension itself: none. The extension contains no telemetry or analytics and does not transfer data to third parties or to the developer's servers.

What the extension does locally: it opens background tabs for user tasks, reads the rendered HTML of the requested pages, removes scripts, styles, and comments, and transmits the shortened HTML only to the лижё.рф website itself. Data processing on the website is governed by the website's privacy policy:
https://лижё.рф/legal/privacy_en.pdf

Removal: uninstalling the extension deletes all data stored by it.