Right, just close it completely and start it again with the command. Btw. I found a solution. If you want me to help you with commands, send me the first 30 lines of your logfile or so, after you started your Nextcloud client (you don't even have to enter your server address). The issue was the ownership of the nextcloud.cfg file in the /home/user/.local/share/data/Nextcloud directory which was set to root, not to my user.