I have the following apps backing up to a syncthing share
- Aegis
- OpenScale
- Gadgetbridge
- OpenTracks
- Signal
all of them were set and forget, except for Gadget bridge who would randomly loose access to the shared
The following apps allow to manually backup to a file, but not automatically.
- AntennaPod
- Catima
- Birday
- Tickmate
No, never had an issue with Signal backups.