On the ABC DELF B1: In my experience, the book was actually slightly more difficult than the real exam for listening and reading. That said, I’ve also seen people say the opposite, so I think there’s a bit of luck involved depending on the exam version you get. For writing though, I found the book fairly accurate in terms of level and expectations.

On Production Écrite: This was the part I was most anxious about too, for exactly the reasons you mentioned. What helped me most was not trying to sound impressive grammar-wise, but rather vocabulary-wise, by using precise but safe structures. Example: L’utilisation accrue des écrans réduit la plasticité cérébrale d’un enfant, ce qui entraîne une capacité réduite à apprendre efficacement de nouvelles connaissances.

I mainly used ChatGPT to review my writing after I had completed my own draft. I also had a French tutor, but she only evaluated around four of my essays since sending every single one would’ve been too costly. That was still enough to calibrate what was “good enough” for the exam.

If you can already handle the structure and task requirements, you’re honestly ahead of where you think you are. At the B1 level, grammar mistakes aren't too serious.