How do I get Kate (or any app, really) to open in a specific location and size, but not have that size and location apply to the File->Open dialog box I subsequently open from that application?

I've changed various settings in the Special Window and Special Application settings for both the main Kate window, and the dialog box window, but I can't get this problem solved.

KDE Plasma Version 5.13.5
KDE Frameworks Version 5.50.0
Qt Version 5.11.1

Running fully updated KDE Neon.

Thanks.

Kate (and other kde libs based apps) accept a --geometry command-line argument which specifies the startup geometry. To force it to always open in that size, you can use the menu editor to edit the application entry for Kate and add that parameter to it's command. (if that doesn't work, you should be able to create your own application entry for it in ~/.local/share/applications by right-clicking in that directory -> Create New -> Link to Application and filling out the details).

Alternatively, Kate's Sessions feature includes the ability to remember the window size and location which can be used for this purpose.

Good idea, but the setting I want is for it to remember whatever previous location and size I gave it. Sometimes I'm transcribing documents, with the image of the document on one side of the screen, and Kate on the other, side-by-side. Other times I want it full screen.

My issue is more with the File->Open dialog using the same properties as the main Kate window, despite using the Special Window Setting, which I assumed would control just that window.

Thanks.

I would assume there should be some additional window properties which can be used to distinguish between the two windows as well.
In the Special Window/Application Settings dialog, on the first tab there should be a button for Detect Window Properties which you can use to select a window and it will fill in the various properties of that window. You should be able to use that to compare and find out what's different.

You might also look into Kate's Sessions as that might also provide you the behavior you want, where you can set up separate Sessions for your different use cases and have it open up in the different positions depending on the Session you launch. There's also a widget you can put on the desktop or panel for selecting the different sessions.