Personally I would not use gimp-plugin-registry package, apart from installing a whole load of old scripts and plugins just for the one you want, as you found some do not work.
I use this one: resynthesizer https://www.gimp-forum.net/Thread-Gimp-2...1#pid11261
Latest gimp_gmic_qt that works with bionic : https://www.gimp-forum.net/Thread-gmic-g...untu-18-04
Flatpak, being sandboxed I found it a bit limiting, although some bespoke flatpak plugins have been added since I last used it, resynthesizer / gmic / BIMP
That is why I use the 2.10.22 appimage
I use this one: resynthesizer https://www.gimp-forum.net/Thread-Gimp-2...1#pid11261
Latest gimp_gmic_qt that works with bionic : https://www.gimp-forum.net/Thread-gmic-g...untu-18-04
Flatpak, being sandboxed I found it a bit limiting, although some bespoke flatpak plugins have been added since I last used it, resynthesizer / gmic / BIMP
That is why I use the 2.10.22 appimage