What type of product should I use to seal/protect the wood interior of a outdoor office?
Well, there's always "nothing" - very quick, low odor, and no gloss to speak of. About as natural as natural wood can get.

Next up from that would be boiled linseed oil, or paste wax, or boiled linseed oil mixed with paste wax. I prefer "bowling alley wax" as it does not have the abrasives that most "floor wax" does, and clear .vs. amber as I don't want to change the color of the wood.

If you are wanting to "seal" it I suppose there are deck "sealers" that are clear-ish, but they are primarily exterior and may not be particularly low-odor (and at core, I suspect they are silicone &amp; wax in a carrier of some sort.) I'd rather just wax it with paste wax.