I got a STEP notification today for the UK with this title: United Kingdom Travel Advisory: Level 4: Do not travel, July 19, 2021.
This is the first paragraph: Do not travel to the United Kingdom due to COVID-19. Exercise increased caution due to terrorism.
This link titled "Level 4 Travel Health Notice for the United Kiingdom" is embedded in the notification: https://wwwnc.cdc.gov/travel/notices/covid-4/coronavirus-united-kingdom
That link has detailed information on what to expect.
The STEP notification also says, "Country Summary: Terrorist groups continue plotting possible attacks in the United Kingdom. Terrorists may attack with little or no warning, targeting tourist locations, transportation hubs, markets/shopping malls, local government facilities, hotels, clubs, restaurants, places of worship, parks, major sporting and cultural events, educational institutions, airports, and other public areas.
There is also a risk of isolated violence by dissident groups in Northern Ireland, focused primarily on police and military targets."
You might want to sign up to get STEP notifications yourself. Here's the link to do that: https://step.state.gov/STEPMobile/Default.aspx