There are a few threads on the forum mentioning that there is an “experiment” way to get the app to sync with other cloud services.
It’s under “Other Sync Services” on this page:
https://community.findingsapp.com/t/dropbox-sync/68
We have unlimited google Drive here at the U and I’ve also been hit by the Dropbox devices limit, so I definitively feel your pain. It’s a shame since Dropbox has been superior to all other solutions for us, but their lack of any intermediate option for syncing (they immediately jump to a fairly pricey tier), is not helping :-\
Corentin