I want a layout (with a sidebar) to be used on two different content types, and also on some views (URLs).
When I added the URL condition to the existing Content Type condition, neither worked.
Is there a way to define an OR condition rather than an AND condition? Or did I just make a mistake in my setup?
node/% + Content Type worked on it's own.
The visibility conditions you can add to a layout are AND conditions: they narrow the applicability of the layout.
You can achieve OR functionality, like using a layout on multiple diverse paths, with Layout Wildcard module.