How to force all programs in Linux to use the same dialog boxes?

Question

linux

Hello!
I noticed a strange thing in my DE. Installed lxqt. Everything was fine, but then something broke. In general, the dialog boxes for saving a file in chrome, mozilla and geany are different from each other. I've looked all over the net and can't figure out what the problem is. At first I thought that the browser settings are like this, then I created a python script and got the same result.
Dialog python script:

Dialog Geany:

Created a ticket on github , but to no avail.
Also tried writing:

xdg-mime default pcmanfm-qt.desktop application/x-gnome-saved-search
xdg-mime default pcmanfm-qt.desktop x-directory/normal
xdg-mime default pcmanfm-qt.desktop x-directory/gnome-default-handler
xdg-mime default pcmanfm-qt.desktop x-scheme-handler/file
xdg-mime default pcmanfm-qt.desktop inode/directory

But it didn't help either.
Who worked with GTK, can you tell me what the problem is? Why are window styles different from each other?
UPD.
I sort of understood.
Geany uses Gtk2 and my python script and Firefox and Chrome use Gtk3.
Qt has its own dialog box. There is also kdialog which opens its own interface.
Here is an example python script for Gtk2 .
Programs using different graphics frameworks will have different dialog boxes.
In general, this is strange. The system is the same and it should look the same.
How to force all programs to use the same dialog boxes?