Flatpak is stable and widely used, but it still has some pain points when used in certain environments or for certain ends. However, most of those drawbacks are being worked on, and fixes are planned.
I’m talking about the executable binary flatpak, which is the interface used to execute and manage applications distributed in the Flatpak bundle format.
Flatpak doesn’t have a UI? It is a packaging format.
From https://docs.flatpak.org/en/latest/introduction.html#terminology
You might be thinking of AppImages, which are more of a pure file format.
Are you talking about theming?
I’m talking about the executable binary
flatpak, which is the interface used to execute and manage applications distributed in the Flatpak bundle format.https://docs.flatpak.org/en/latest/flatpak-command-reference.html#flatpak