I needed to pass C1 German exam recently and my vocabulary was a bottleneck. I also wanted to learn words in context + using interesting texts, which I would enjoy reading. Thus, I made VocabBoost - https://vocab-boost.online/ - a Chrome & Firefox extension to make a language test out of any website.
I think the problem with other suggestions is that they help you practice your passive vocabulary (i.e. understanding a word). I don't think this would help with actually using words in your writing. In order to use a word, you need to actively map it from the current context (because that's effectively what you do when you write). That's precisely what VocabBoost does. You read the text (see the context) and it asks you to fill in blanks (can be multiple choices test to simplify the task) - i.e. actually use a new word.
I am still developing the extension. Feel free to reach out if you have suggestions.
I could add "tricky words" mode :)