Yes. If you step on land anywhere in Antarctica, including the islands you'd normally visit, you have made a continental landing. The idea that only the mainland counts is a distinction that leaked out of the Antarctic Treaty's messy definitions and into cruise marketing, and it doesn't hold up. Most of the accessible, wildlife-rich sites are islands sitting on the same continental shelf as the mainland.
The geologist's framing is the cleanest one: touching the continental shelf or the seabed is itself touching the continent. Islands like Adelaide connect that way, and glaciers that once joined places like Stonington to the mainland have retreated, which would move the goalposts anyway.
There's a good reason most landings are on islands, and it isn't that the mainland is off limits. The mainland coast is heavily glaciated with ice cliffs running straight down into the water. The islands are easier to land on and far richer in wildlife.
Guides do attempt a mainland landing on most trips. Whether it happens depends on weather and site availability, and only one ship can be at a site at a time. The myth is unhelpful partly because it funnels pressure onto a very small number of mainland sites.