1.21 was a pretty massive update in multiple regards, not just from Mojang's own changes in 1.20.5 and 1.21 but also due to the Forge/NeoForge split primarily taking effect in it. This makes it difficult to port all around, especially for a mod as big and complex as Quark
The devs are working on it as they can, they only have so much time to dedicate to modding when paired with their personal lives. It'll happen eventually, just need to be patient for it