I was using the elements list up until yesterday at noon, and I would come out of Focus mode, and I could use the elements list to access things such as jumping to messages, very fast.  However, this just stopped working and now I find the Slack app much slower to use. 

I found the following articles on the Slack website, which may be of use.

Use a screen reader with Slack on desktop
https://slack.com/intl/en-ie/help/articles/360000411963-Use-a-screen-reader-with-Slack-on-desktop

Keyboard accessibility in Slack 
https://slack.com/intl/en-ie/help/articles/115003340723-Keyboard-accessibility-in-Slack-