Thank you for looking into this! It would really suck if the sfw version were banned in Germany, there's no reason for it I can think of and unlike other banned games I can access the sales page and view the price, but not proceed to check-out. This has never happened before. Also, the sfw version of Synthetic Lover is still available on Steam and I can put it in my shopping basket and proceed to check-out with my cart showing the correct price (not 0.00 € like it does for The Symbiant). It would be awesome if you could try to get to the bottom of this.
It's just endlessly frustrating to be a fan of visual novels living in Germany in this day and age. :( I am so grateful you sell your games through itch.io as well.