Desktop client linux

I’m not able to access my nextcloud server via the linux desktop client. With a browser it is working fine, but when I try to connect with the desktop client for Linux (Linux Mint 19.1)

Adding own server address (https://my.server.org/nexcloud)
New window opens with “re-open browser”

within the browser window I add my username and password
Next window is “Kontozugriff” -> give access to the account
and than nothing else happens.

My nextcloud installation is 17.0.0

My Owncloud client for linux is running well.

Hi,

My Owncloud client
Is this a typo and you meant Nextcloud client or really owncloud?

Did it work at some time before and failed just recently after an update?

Not really, the sync between a nextcloud client and my nextcloud server never works. With the owncloud desktop client or sync app for IOS it works always.
Now I removed my reverse proxy and change the settings for direct access it works. But with a reverse proxy and the ProxyPass rule not.