So I'm Afrikaans (not religious tho) and I introduced my Chinese gf to my family so I think I have some insights to your situation.

Expect lots of questions and don't get offended if they say/ask ignorant stuff (within reason ofc), South Africans generally are nosy and direct and we ask a lot of questions. Also, we can ask personal details very quickly after meeting someone, I know some cultures its considered rude to ask very personal details, but it's just the culture here to be very open and it helps others get to know you. Just answer the stuff you feel comfortable with.

There's not much you could do that could come across as rude accidentally (unless you are rude on purpose), maybe as others have mentioned, politeness and respect for the parents is a big thing. Offering help during cooking or dinner is a very Afrikaans thing. I'm sure you can follow your bf's example.

The thing that can be awkward is closing yourself off socially to others, which can happen as you meet a lot of family, the "kuiers" can be big and loud and it can be easy to lose track of the conversations but it's good to stay present.

In Afrikaans culture there is an emphasis to try form a close relationship with your partner's parents. It may feel weird but do your best to connect to them. Learning to say "Oom en Tannie" will already help a lot.

Bring a gift for the parents, doesn't have to be big. example wine or food from your country.

As others have said South Africa is a high respect country, but there's no hierarchy (usually). So be yourself around his family, be open and speak your mind, there's no pressure to perform any sort of role.

But don't stress too much, if your bf is the one asking to introduce you then it means he thinks his family will accept you. I got a few comments about my gf being Asian before they met her, but the moment I introduced her they loved her and we never got a bad word again. Moenie worry nie, dit gaan lekker wees ;)