I've noticed a sharp deterioration of the "Page Experience" Score from Google Search Console (for the Hebrew Wikisource), starting September 1st:
A quick investigation pointed to Central Notice banners, specifically the Wikimedia Soundlogo Contest campaign. According to Lighthouse estimation, the banner adds to the Cumulative Layout Shift about 0.6 seconds. The banner images lack width/height properties, which should be fixed.
The delayed CLS severely impacts page visibility.