The macOS app does not give me any option to choose how I can sync my files. What can I do?
If you’d like to use OmniPresence, there are steps in https://support.omnigroup.com/documentation/omnioutliner/mac/5.2/en/working-in-the-cloud/ to get setup. Using OmniPresence with Omni Sync Server is a popular way to keep your files synced. The article includes directions for using other cloud services if you prefer as well.