Hi, I have had my D&D notes synced between my phone, and two computers. I tried to open my notes on my phone to find them far out of date, and opened sync thing to see if I could adjust that and instead it decided that the older phone files took prescience and reverted several files to their much older versions, and as both computers and the server are online, all of them synced and I wanted to see if recovery was possible or if years of work are gone to this error
Unless you have enabled File Versioning on at least one of the computers, you cannot really do anything about the deleted files within Syncthing. If you have no backups, then the only way would be to use some kind of data recovery to restore them.