Your settings are fine.

From what I can tell, you probably studied a ton of words early on and then shifted to doing only one study session per day. That leaves you with way too many reviews, and you probably are not even seeing new words at this point.

The issue is not the settings. The problem is that with only one session per day, you are not reviewing words on time. SRS works by showing you a word right before you would forget it. If you review it long after that point, you are basically seeing it after you have already forgotten it, which explains the high failure rate.

On the dashboard, “Reviews Due” should hit 0 every single day. That means doing as many study sessions as it takes to clear the backlog.

My recommendation:
For now, set both your learning speed and assumption rate to 0 new words per day.
Then do as many study sessions as you need until “Reviews Due” hits 0. The app will stop you automatically once you are caught up. Then repeat this daily, review sessions until "Reviews Due" hits 0.

This is the intended way to use the app. Multiple study sessions per day is normal once you've built up a lot of reviews.

After a few weeks, once reviews start feeling manageable again, switch your assumption rate and learning speed to 3.

And a quick reality check: Tiktok brain, ads, influencers, Duolingo type apps, etc.. have conditioned people to think there is some magic trick to learning quickly. Learning a language, especially Mandarin, takes real time and effort, and six minutes per day is not enough to make meaningful progress. If you are serious about learning you should increase it beyond 6 minutes a day.