Hello Team,
I’ve just upgraded my test Nethserver to version 7.9.2009. On this test server I’ve installed Nextcloud so with this Nethserver upgrade I also receive a Nextcloud upgrade to version 20. After the upgrade to 2009 I discovered I have a blank dashboard on my Nextcloud after I login. After a bit of searching I found that this problem may be related to the Accessibility App being disabled. Since I have a blank screen upon login for Dashboard I had no way to access my Apps page using so I had to change my URL to include the following so that I can see my Apps page. So I added the following - /index.php/settings/apps
so my full patch would be:
https://mycloud.mycompany.ca/index.php/settings/apps
Now I can see my App page and enable the Accessibility App once again and now my dashboard works.
There is also a way to enable an App using the command line but hopefully the above method is easier and works just as well.
example: enabling calendar app
sudo -u apache scl enable rh-php73 – php -dmemory_limit=512M /usr/share/nextcloud/occ app:enable calendar
Hope this post is useful for anyone else who may be upgrading and disabled the accessibility app. 
Cheers!