Welcome to SpeicherBox.ch Client for Ubuntu.
Tested on latest stable version of Ubuntu (v20.04) and also on Ubuntu v18.04.

For installation run these commands in Terminal:

Ubuntu v20.04
sudo add-apt-repository ppa:seafile/seafile-client
sudo apt-get update
sudo apt-get install seafile-cli 
sudo apt-get install gdebi-core 
sudo gdebi /<deb package location>/Speicherbox.ch_v7.0.7.deb

Ubuntu v18.04
sudo wget http://ftp.de.debian.org/debian/pool/main/g/gcc-10/gcc-10-base_10.1.0-2_amd64.deb && sudo dpkg -i gcc-10-base_10.1.0-2_amd64.deb
sudo wget http://ftp.de.debian.org/debian/pool/main/g/gcc-10/libgcc-s1_10.1.0-2_amd64.deb && sudo dpkg -i libgcc-s1_10.1.0-2_amd64.deb
sudo add-apt-repository ppa:seafile/seafile-client
sudo apt-get update
sudo apt-get install seafile-cli 
sudo apt-get install gdebi-core 
sudo gdebi /<deb package location>/Speicherbox.ch_v7.0.7.deb