As a recent LMDE 6 user, I noticed something that never occurred in my previous uses of Linux Mint 20, 21, and LMDE 5.
When I Download something, the pop-up screen appears asking for a location, but the theme of the popup changes and looks like an older version of Windows. I use a Dark theme and the Download screen is Light, a different Font, and Font size.
It’s a little disorienting because it sticks out like a sore thumb.
I’m not sure where to start my trouble-shooting. Any suggestions welcome.
Ah! Now I understand. It happens for some tools (specially Python ones) the upload or save option window looks extremely dated.
I never paid attention to it. I think it’s because the application uses some libraries that open some other file explorer instead of the one provided by the desktop environment.
Maybe does it use Qt (PyQt?), while the rest of the desktop uses GTK?
Do you have Qt5 setting on the control panel?
Try change on the first tab:
Style: fusion