Under the adjusted Level 1 restrictions, I believe it is still the case that "Gatherings are restricted to no more than 1 000 people indoors and no more than 2 000 people outdoors". So the carnival events are ticketed to limit attendance numbers and then you move between the events at your leisure (although being at night I would recommend trying to get a taxi, or limit which events you go to after dark). The CBD is 'vibrant' around Long St at night but is also 'edgier'. I suppose in a large group it may be harder for people to approach you but also harder to get away from beggars / scammers and easier to be pick-pocketed. I don't mean to sound negative since Cape Town is a great, vibrant city but you need to be aware it does have issues. As a tourist I would definitely stay in Green Point and take an Uber/taxi after dark to get back from the ticketed events. Also I wouldn't walk through Company Gardens at night usually.