The feature can be found in the edit folder dialog of Syncthing-Fork. There is a slider “Individual sync conditions” which can be enabled and below , you can go to a subdialog and tick which conditions you want to apply to this folder.
Short form:
- set global run conditions, e.g. allow mobile data and wifi.
- edit folders you do not wish to sync over mobile data, turn on individual sync conditions and disable mobile data there.
In the end, there will be all folders syncing on wifi and one folder syncing on wifi+mobile data.