https://screenrant.com/star-trek-banned-episodes-explained/

Though the Star Trek franchise is generally considered safe for viewers of all ages, a few episodes have been banned in the past.

Every Episode of Star Trek: The Original Series That Was Banned in the UK (& Why) (https://www.cbr.com/star-trek-tos-banned-uk-episodes-list/)

For 30 years, four episodes of Star Trek: The Original Series were banned by the BBC and not broadcast in the United Kingdom. Here's why it happened.