This might be a silly question, but when putting an app on TestFlight, do I use xcodeproj or xcworkspace? Can you explain why?
It doesn't matter, you can choose either xccodeproj or xcworkspace, and the step(s) (manually) don't change.
Xcode -> Product (on the menu bar) -> Archive
The distinction is:
xcodeproj is a standalone project.xcworkspace on the other hand, allows you to work on multiple projects. It can contain more than one .xcodeproj. i.e, When using cocoapods.