I wrote a simple script in order to help someone in a recent reply from me, to make running Flatpak applications from terminal easier. After that I worked a little bit on it further and now ended up with 2 completely different approaches.

1. flatrun: Run an app by a matching search filter. If multiple matches, then print all matching app ids instead.
2. flatapp: Show list of installed apps in an interactive menu. Plus show a description of the app in a preview window. Run the selected application. Requires fzf.
3. flatsearch: Show search results from repository in an interactive menu. A selected entry will be installed or uninstalled if it exists already (with confirmation from flatpak). Requires fzf.

# Show all matching apps
$ flatrun F
com.github.tchx84.Flatseal
io.freetubeapp.FreeTube

# Run io.freetubeapp.FreeTube
$ flatrun freetube

# Show help for com.obsproject.Studio
$ flatrun obs --help

or flatapp: (requires fzf)

and new flatsearch youtube (requires fzf)