One pixel 'grab' area when resizing windows

In many window managers, holding the Alt key will make the whole window a big move/resize zone for the left and right mouse buttons, respectively. If not enabled by default, it is usually a setting you can edit.

Grab at the corners. It's substantially larger there.

This is answered here - use the Gnome Tweak tool aka Advanced Window.

Before discovering this I tried 17 themes and none addressed this problem except that in SOME windows I got a slightly bigger area in the bottom right corner which I did NOT have in the shipped themes. All of which is truly rubbish.

Try the top-left and the top-right corners, more grabblable than the bottom ones (which are almost impossible to get...)