If I Write Novel While Working at Google Does Google Own My Manuscript?

I'm not a lawyer. In my brief time there years back in the US, there was a training course that somewhat touched on this. Essentially the takeaway was that what you developed on your own time and equipment was a bit of a grey area, but likely problematic if what you were building was something that would compete with Google in some way. Since Google owns so much tech in so many spaces, the general argument was that whatever software you were writing on your own time was likely something that could be seen as competing with Google, therefore you'd be better to just avoid it altogether.

I'm not sure if the same argument can be made for non-code manuscripts.

It depends in the country. The UK differs significantly from the US in this regard. I believe (but I am not a latter and I am happy to be corrected) in the UK that unless your job specifically is to produce that kind of product, it is still your property. Conversely, if you are paid to come up with novel chemical engineering designs and you come up with one out of work time, they still own that.

Clarification (thought it was obvious): when I'm not clocked on. But on in my own time, on my own hardware. Not in " work hours"

The only person who can confidently say Yes/No is a solicitor who reviews the contract.

It's usually in the contract that anything you do on company time is property of the company. I have a feeling they'd be more concerned about the time theft than selling your my little pony fanfic.