I resolved my issue with Nextcloud!
That was the file ‘config.php’ into ‘/srv/my_disk/nextcloud/config/’ that I have badly modified. 
Unfortunately, I had followed another help.nextcloud advice https://help.nextcloud.com/t/solved-internal-server-error-memcache-not-configured/38255/21 thinking that this would resolve my problem. I shouldn’t have do that.
So I resolved my issue removing this code from config.php file:
‘htaccess.RewriteBase’ => ‘/’,
‘memcache.local’ => ‘\OC\Memcache\APCu’,
‘memcache.locking’ => ‘\OC\Memcache\Redis’,
‘redis’ => array(
‘host’ => ‘localhost’,
‘port’ => 6379,
),
After refreshing my webdav Nextcloud page, I found again the user login of Nextcloud. On this page, it was proposed to update my Nextcloud version, and I accepted it.
The update goes on and after a few minutes, the view of my Nextcloud dashboard cames up.
All is working fine! 
Thank you @Mageunic to have tried to help me.
Finally that was config.php file that wasn’t correct, but on some other parameters than the login.