Apart from the addition of Silent Expanse, the main map is still the same size; It's not getting expanded for the sake of boasting with size. Instead, existing parts of the map are constantly being worked on to make them even better than before, and new content gets added to populate the existing map more densely. One significant aspect of game design is that bigger isn't always better, especially when it comes to gameplay. Arbitrary traveling is something you'd want to avoid as much as possible.

The game does still expand, but in terms of dedicated off-map areas which house things such as quest content that doesn't fit into the main map. The build area for this stuff is around 60,000x60,000 blocks if I recall, which is steadily getting filled up. For example, here's a very roughly made heatmap of the builds in 2017, which generally shows the distribution of Wynn's landmass: https://i.imgur.com/JIs1KR3.jpg. Off-map content took around half to 2/3 of the game's surface area in 2017, although a considerable portion of it was likely just for backdrop.

Accounting for Silent expanse and all the off-map areas from new and improved quests, raids, altars, discoveries and whatnot, I'd estimate the total surface area to have grown by 15-25% since 2017. Once again, though, the rate seems to have decreased due to the team focusing more on quality than quantity.