On second thought: thank you @fiftyfourthparallel for originally pointing it out and thank you @enmus for making me finally see it after I was too dense to see it the first time:
It is obviously a bad idea to mount an encrypted partition inside an untrusted qube. It’s bad practice and bad advice.
I will edit both in the forum and on my website to correct this mistake in the next days.
At the time, your post stuck in my mind, and I posted it yesterday because I read the docs again (and constantly over and over again) and stumbled upon this, and I had no doubt how you’d react, but I needed it to create that way for users hopefully an example of a good practice of a constant re-reading, re-thinking and revising, eventually to realizing what many of us already did: that Qubes is life-changer, milestone.