I use a similar case, and love it, but my pen is at the top, and super easy to grab, even if you don't have fingernails.

https://www.amazon.com/dp/B096V6G4TV

However, as for writing, it's probably just as stable as the one you presented. I.e., not very. More for media consumption, where you won't be pressing on the screen too much or need accurate pressure sensitivity.

Maybe you need a tablet stand:

https://www.amazon.ca/gp/product/B09P87NBYS

https://www.parkablogs.com/content/review-parblo-pr100-tablet-stand