The Stone Giant can be encountered and defeated after the recent update, but the Black Board in Flayk's inn refuses to reward the player for the quest's completion.
By the way, there was an even stronger hint about you being German: Only being able to examine sign posts from the front seems to be a big thing in the German RPG Maker community. ;)
I'm slowly chipping away at the end-game content, so expect a few more posts from me in the following days. There are still a lot of loose ends, e.g. not being able to enter the Stormy Prairie (Western Edge western path) or the cave on Victorious Meadow, but I'll post a more comprehensive list at a later point, while I hopefully reduce the number of loose ends as I advance towards the game's ending.