GnuCash with (optical) PhotoTAN?

With Ubuntu 20.04.1 I now installed GnuCash – both as Flatpak (version 4.1) and from the official repos (version 3.8) and am nothing less than flabbergasted that online banking still won’t just work again. With 2-factor-authentification, I’m being prompted for the PhotoTAN without being presented an image to scan. There’s a Python script which was last updated about a year ago to presumable tackle that issue. There are hints to the fact that the sandboxed Flatpak installation might need some extra tweaks to display the PNG.

I don’t mind if its version 3.8 or 4.1. I just want online banking back. Any guidance much appreciated (or at least encouragement to try and use either the abandoned (?) Python script or the sandbox tweaking).

What a bummer.