Ok, sorted out the problems with my Amiga music file-> UADE-> Flac -> NAS conversion script.
I toyed a bit with gbsddialog, bsddialog and gum but eventually I stuck to kdialog for the time being, because it feels native on Plasma 6.
I could fix the problem, and as always it was a stupid bug... (kdialog using qt6 and forgot the script used dbus-qt5...). So, the gauges/progressbar's now working again.
all is well...