Time is a flat circle, and has new content. Developer Cyan Worlds had added another area to its modern remake of the classic 1993 adventure game. The expands the game with a "snowy, mountainous seascape", which becomes available to players after completing the main story of Myst, bringing "all new narrative beats, new lore, and new sights to behold".
We should pause a moment, however, to clarify what "new" means here. The world of Rime is indeed new to Cyan's contemporary overhaul of Myst, but the history of this island stretches back a quarter of a century. While Rime never appeared in the 1993 edition of Myst, it was introduced in 2000's , which converted the game from pre-rendered images into full realtime 3D.
As for why Cyan has added it into their modern remake, it appears the community has been requesting it, with the developer proudly proclaiming, "You’ve been asking, and we’ve been listening." Alongside adding Rime, the update makes several smaller additions to Myst, updating DLSS support to version 4.0, adding a zoom function, and making some "visual improvements" to the Myst island library.