I really wish Americans would just stop with this.
I’m a Brit. Married to an American for a quarter of a century.
Not only have you not scratched the surface you’re also simultaneously wrong.
Pants as one tiny example. Where we live, near Liverpool, pants will mean trousers. Just as it does in the US. In fact much of the North West of England uses vernacular that might be more familiar to Americans than the rest of Britain.
Then there’s phrases like ‘just about’ or to ‘table an idea’. I’m not even going to get into those. They took my wife and I an age. The latter even caused significant problems in the second world war because of its diametrically opposed meanings.
Look. The only piece is advice you can give an American moving to the the UK (cos trust me we’re WAY more familiar with your vernacular than you are with ours.) is shut up and ask. Never assume.