Is there a way to see a report on the two versions of a landing page broken out by desktop/mobile? I would like to see how the mobile version is performing vs. the standard version. Is this built in somewhere/accessible?
No, sorry.
You can try to extract a count by using a smart list with
Visited Web Page on Browser constraint between certain dates.
There isn't no - it's a real pain as well considering that Marketo is pushing an "everything everywhere" message but the way to report on it is not ideal. To create the Smart Lists to do this you need to create quite a few of them as each browser / Agent ID have subtle nuances.