(1) I put a project on a USB thumb drive and edited it at home. But I forgot to bring it to office the next day, so I ended up working on a second copy of the same project (but editing different parts of it). Now I have two slightly different project folders. How can I sync the two?
(2) I see in the manual there is a big section on syncing between MacOS and iOS through DropBox. Does the same procedure apply to syncing between two MacOS computers, say office and home? Anything to watch out?
I’d open both and compare & copy the latest changes over (manually). Could be a very unsatisfying answer depending on the extent of your edits.
Kind of. The biggest difference is that iOS Scrivener doesn’t need Dropbox (as an app) installed, but macOS Scrivener does. So every macOS (or Windows, etc.) Dropbox installation counts towards Dropbox’s three devices limit for their free tier.
Other than that… give Dropbox time to sync. Don’t shut down a computer until it’s done syncing. Same on the other side. Let Dropbox download the changes before opening a project. Don’t open the same project on different computers at the same time. Don’t allow Dropbox (or even macOS) to “optimize” your storage (moving files from your local drive into the cloud). Sounds a bit scary, but with keeping those things in mind it’s a pretty stress-free experience.