After some test in my Elementary OS 5.1 maybe you need have this packages
For the line
(pcloud:3274): libappindicator-WARNING **: 19:22:30.549: Unable to get
the session bus: Unknown or unsupported transport “disabled” for
$ dpkg -s libappindicator1
Status: install ok installed
Same issue here, adding to this with more info;
sideloader is installed
old flathub ppa removed
I'm able to install a flatpak via terminal.
This allows the app to be displayed in applications
Once installed it can be launched from applications but the application fails to run and just sits in the dock > after clicking the app in the dock it ...
Installing libreoffice-impress standalone seems to not bring all the required packages for it to look properly (and I suppose work properly as well?):
So I suggest removing LibreOffice Impress, and installing the full LibreOffice bundle.
sudo apt remove --purge libreoffice* -y
sudo apt install libreoffice
After the install is done (it might take a while), ...