dialogues showing up in the bottom left corner of the display

I'm running Debian/Forky on an AMD64 system. I'm using the Plasma 6 
desktop over X.

For the past while (months at least) most dialogue windows show up 
barely on the screen, at the bottom left of the display with just a 
millimetre or two of the top of the window frame showing above the 
bottom panel. This makes it hard to even grab the frame to make the 
window visible.

I assume it has something to do with the very bad idea to remove 
standard window behaviours, like remembering application sizes and 
positions, and making us set them on a window by window basis as part of 
the move to the already long in the tooth yet somehow still not ready 
for prime time Wayland.

Maybe it's just me, but I really only want application windows to 
remember where they were and what size they were. I expect movable tool 
windows (e.g. Scribus properties) to do the same. Pop up dialogues I 
want to be centred in the application that launched them (or in the 
centre of the screen - just somewhere where I don't have to look for them).

  I'm amazed that after 40 years of development, that I even have to ask 
for a simple way to do something like that. Yet somehow we're now at the 
point that I have to move applications to the correct  virtual desktop 
and close down multiple instances of other applications after logging in 
because the window manager can't handle that anymore.

Most things I can live with, but how can get all the pop-up dialogues to 
appear somewhere where I don't have spend time dragging them to a 
visible place on the screen?

Thanks.