Just yesterday I added myself as a co-maintainer besides Safihre on that package from SynoCommunity. Current version v1.14.0 is in the pipeline, see syncthing: Upgrade to v1.14.0 and ignore folder permissions by default. by acolomb · Pull Request #4527 · SynoCommunity/spksrc · GitHub. I’ve also been involved with the last couple of releases there. So at least you see there are real people working on it, and they can be reached 
There is also a build made available through Kastelo, Inc., where @calmh, Syncthing’s head maintainer is involved. Some people prefer that over the SynoCommunity version for its different update policy. See New package for Synology NAS for that effort.
EDIT: I’m using the SynoCommunity package on two DiskStations and several laptops in production, so can definitely say it works reasonably well for my needs.