I’ve created a course entirely on my mobile. I used to be able to edit the course description as well. I use the description to inform other learners about the progress of the course since I create the course simultaneously to the progress in the textbook we make in my class.
Now, it’s not possible to edit this anymore from my android phone. If the website is supposed to be be mobile friendly this should work too.
Have you tried switching to “desktop view”? Depending on your (mobile) browser and your environment (like Android, iPhone, etc.), the approach might vary though. I see you’re on Android. If you use Chrome, tap the (vertical) three dots on the top right and tap/tick the “Desktop website” menu item. From there you should be able to do whatever you can on a desktop (PC) or Mac.