What is Shadowban?
Shadowban is the popular term for an unannounced restriction: the account keeps posting, but the content stops appearing in Explore, hashtags and recommendations. Meta does not use the name, but it has "account status" in settings, which shows whether any content was flagged as ineligible for recommendation. Common causes are violating recommendation guidelines, using browser automation or engagement bots, and spam-like behavior such as mass commenting. A good share of reach drops, though, is just content that stopped performing.