Hi there ! 
I have installed the Flatpack, configured it and realized the app is not working properly.
Once removed, I installed the AppImage provided.
But the configuration seems to be remanant and the folders sync are not showing up anymore. Though, when I want to reconfigure it, it says the folder chosen is already configured…
Now I am trying to remove all configuration from both AppImage and Flatpack, but it does not change anything.
There is a remaining configuration file somewhere that messes up any method of installing the client.
Can you assist me please?
I used the AppImage documentation to remove the files in ~.local and ~.config folder of Nextcloud.
For the Flatpack, I used the configuration remove integrated in Discover (KDE app store).
Info:
Operating System: KDE neon 6.2
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1
Kernel Version: 6.8.0-51-generic (64-bit)
Graphics Platform: Wayland