This is a bit of a "how long is a piece of string" question. Depends on context. but things that me or other people I know have found different between South Africa and here include (this is just a top of my head list, not definitive or prescriptive):
The service industry is huge and it can be hard for non South Africans to understand how to interact, pay, tip etc. It can be confusing understanding why someone is packing your shopping, filing your car with petrol, directing you where to park etc etc and when and how to thank/tip. The glaring inequalities and poverty also impact things, creating interactions you would be very unlikely to have in this country.
South Africans have a reputation for bluntness and directness. This will present differently in say a white South African man vs a black South African woman, but it is nonetheless a defining feature and largely true. We are opinionated and direct.
Expectations around polite social distances/social interactions are different. English people can find it quite odd when, for example, at a restaurant, a random person will turn up at the table, pick up a toddler and wander off to a soft play. That person is probably employed by the restaurant, but that's not guaranteed. Similar situations will take places on beaches, in shops and so on. Similarly, a casual conversation can be more animated, more tactile etc than is standard or normal in the UK.
South Africans are generally very hospitable AND in Cape Town can be quite closed off and unfriendly. These two contradictory things can be true at the same time.
Bureaucracy is different and weird.
Broadly, and this is not definitive at all, but, days start and end earlier as a rule, particularly in Cape Town. That applies to working hours, school, social activities etc. Although in summer, sunset is also the defining time differentiator - activities happen pre sunset or after sunset. Also, no one specifically says that, making it very irritating for non Cape Townians trying to pin things down.
Cape Town car parks all completely throw you and take years off your life as no one in Cape Town can drive in car parks. The rules of the road cease to exist there. 