libgconf-2.so.4 available on Endless or not?
Why i ask libgconf-2.so.4? Since there is no Flatpak version of Vivaldi, i try to install Vivaldi on Endless with this way https://gist.github.com/ruario/8f648cc3069d1a55d9c8, but the installation ended with error below.
Unfortunately libgconf is pretty obsolete, and we don’t have it on Endless OS. Many Linux distributions do still have it available, since it used to be an essential component — but we launched Endless OS only after libgconf was already obsolete, so it’s not available.
Ideally Vivaldi would stop using it 
If that’s not possible, then the best option is probably to create a Flatpak which includes libgconf in its environment. I would not be surprised if some other Flatpak has already done this, since Vivaldi is probably not the only thing that still uses libgconf.
Yep, you could quite easily make an ‘extra-data’ style flatpak for Vivaldi, which downloads their binaries and unpacks into the Flatpak container. There are a number of flatpaks on flathub that have gconf available since Chromium still needs it - if you import the electron baseapp that’ll be a quick start since that includes gconf.. The spotify app is a good example of how to do this.
If you’ve got more questions about making flatpaks, feel free to ask.
Get this error starting Popcorn Time, any ideas?
/opt/popcorntime/Popcorn-Time: error while loading shared libraries: libgconf-2.so.4: cannot open shared object file: No such file or directory
The solution to your problem is probably similar to the solution above for Vivaldi.
Yep - this is true of any app that is based on Chromium (at least until they upgrade).
For what it’s worth Butter, which is a successor project to Popcorn Time, seems to have made at least one flatpak release: https://github.com/butterproject/butter-desktop/releases I haven’t tested but it should work.