With a screen reader turned on, the "Open All/Close All" buttons do not convey to the user that the page content has changed on the page after clicking them. 

Users that are blind need this information to understand the state of the page.

Suggested fix is to [dynamically manage aria-expanded="true/false".|

https://www.w3.org/TR/wai-aria-practices/examples/disclosure/disclosure-navigation.html]  (which I think is what you already have in place for individual sections-?).

We tested this with NVDA/Firefox, Moodle 3.10.6, Collapsed Topics 2020110906.

We are happy to help assess any possible solutions or provide whatever support might be useful. Thanks!