Total Commander

Please add the parameter setting the thickness of line for "to show cursor in the target panel" - InactiveFocus.
When viewing images:
In the thumbnails view (CTRL+SHIFT+F1) and when the target panel is quick view (CTRL+Q) sometimes I need to switch the focus to the target panel, but then it is very difficult to visually find the focus on the source panel (where thumbnails view) in the variety of colors. I tried different variations of colors and types of lines (as described in the help), but this does not help.
I think setting the line thickness will help in this case.
It may even be better to do this specifically for the Thumbnails mode.

but then it is very difficult to visually find the focus on the source panel

If you just press the Tab key the cursor will automatically go to the focused file in the thumbnail view side.

I thought of such an offer. But I mean when only a mouse is used without a keyboard.
I also know that I can click on the address bar of the source panel with the mouse. But still, the desire is simply to increase the thickness of the frame line.

TwinKey allows to paint the current element in an inactive panel into a beautiful gradient with excellent visibility.