Eight Grade has a 15 rating in the UK.
Here's the BBFC (British Board of Film Classification) listing for it: https://bbfc.co.uk/releases/eighth-grade-2018
The ratings info says this:
> Language
> There is strong language ('fk'), as well as milder terms (for example, 'dick', 'shit', 'goddamn', 'God', 'Jesus Christ').
> Sex
> There is a scene in which a web search shows a woman explaining a sexual technique, accompanied by strong sex references.
> There is also a scene in which a young teenage girl suffers a panic attack, as well as one in which an older teenage boy tries to pressurise a younger teenage girl into having sex; however, she does not agree to this.
I don't know enough about BBFC to say which of these they place more importance upon.
(Eighth Grade is a very good film btw, and A24 are currently my favourite film production / distribution company).