Eeschema / File / Page Settings.
Pcbnew / File / Page Settings.
In both you can select “custom size” and type in some numbers of the size you want.
You can also define your own custom page layout and use that for your projects.
I find the title block on the pages much to big, and you can apparently remove it or make it smaller on a custom page, but I have not yet bothered to figure out how to do that.
In the KiCad Project Manager there is a “Page Layout Editor” for this, and it starts OK, but beware that you have to figure out where to put your custom page layout. The default pages are very likely in a read- only directory.
Just made a custom layout, by simply taking an existing and removing all borders, so only the title block remains and saved it in a custom location. Then put it in an existing drawing and it works as expected.
I also never ever use scroll functions in KiCad. I find it much more effective to zoom out with the scroll wheel to get an overview, and then zoom in again on a more interesting location.