Currently in version 0.400, after completing the main story part in the Fertile Forest (Dryads + Abandoned Temple), the Main Quest just disappeared for me. The Dryad tells you to go South IIRC and I got a notification for a new quest, but when I check the quest log, the Main Quest line is no longer there.

Anybody know if it's possible to continue the story from here, or is it just softlocked at this point?

After exit the forest to world map, head south then go west. There should be a beach where you can find a purple hair guy in a booth on top side of the map. He can take the MCs to the Amazon island where you should be able to continue the story.