How can I review the set-up & config used for a flatpak app?

Question

I am having some issues with a few apps installed using flatpak. In trying to track-down what to look at and what questions to ask, I have been trying to identify how to view an installed app's configuration and set-up data.

Some basic things that I think should be accessible include:

• What runtime environment does the app use (or is it require)?
  • According to the man page I can use flatpak run <runtime>
  • "If REF names a runtime, a shell is opened in the runtime. This is useful for development and testing." ... man flatpak-run
  • I would need to identify the runtime that the installed app wants to take advantage of that tool.
  • I tried listing them, I got 17 runtimes to consider

    $ flatpak list --runtime | wc -l
    17
    $ flatpak run org.gnome.meld.Locale
    bwrap: execvp /bin/sh: No such file or directory
    

  • My thought that the runtime meld uses was org.gnome.meld.Locale was a bust
• Is there a default or generic runtime that apps normally use?
• The list of runtimes shows a few 'org.freedesktop.Platform.XXX`; where might I find documentation or descriptions for the platforms?
• I am currently getting assorted errors about/from running apps that look like environment or set-up issues, e.g.:
  • ERROR: ld.so: object 'libgtk3-nocsd.so.0' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.
  • Gtk-Message: 12:24:27.112: Failed to load module "xapp-gtk3-module"
  • ERROR:sandbox_linux.cc(377)] InitializeSandbox() called with multiple threads in process gpu-process.
  • ERROR:bus.cc(397)] Failed to connect to the bus: Failed to connect to socket /run/dbus/system_bus_socket: No such file or directory
  • ... it can be a bit boring.
• Does flatpak have a information command to show the configuration (like a docker info command)?
• If that's not possible what should I look for if I can find the app's build area on github or whereever?
• Do flatpak apps have anythingn like a requirement listing?
  • Somethings are opaque or even mysterious. By trial and error I discovered that meld needs access to /tmp.
  • Well of course. Thank goodness for flatseal.
  • The thing missing in my opinion is a dependency or requirements list for the installed app.
  • Plus how/what configuration to provide. A case in point woudl be the error about accessing a bus above. Which bus? What kind of access?
• Here is a BIG issue for me. Is there a method/option to specify limits or quotas on a flatpak app while it is running?
  • Some flatpak apps have been seen to use 90% of memory. They get clobbered.
  • I'd like to limit the page set or memory quota
  • I'd like to limit things like disk usage or output file size, etc.
  • If there is some internal bug to flatpak or these different apps; it is better to set limits and see what area might be the source or trouble.

Hoping some flatpak afficionados can point me to relevant documentation or how-to posts so I get make some headway troubleshooting some of these problems. Looking forward to suggestions.

• x