You were asking for synching savegames and savegames are typically just a bunch of files.
All I need is a file sync tool. And I want to control it myself. I don’t even want a program using some database fed from people I don’t know which then leads to file uploads from my computer from arbitrary directory locations.
Sure, finding file locations is not everyone’s cup of tea 
But it isn’t hard. And you don’t have to sync a whole directory, proper sync tools allow filters like wildcards (e.g. *.sav; *.s??).
ScummVM savegames only work for games supported by ScummVM.
GOG Galaxy only works for games installed using GOG Galaxy.
Steam only works for Steam games.
A custom implementation in Broken Sword, Broken Age etc. only works with that particular game.
Also they may be using cloud storage I don’t trust, no encryption etc.
Generic file sync always works. And I need it anyway for all other kind of files I want to have synced between devices. Savegames is just another use case.
I see. SyncToCloud really seems like a good solution for you. It’s multi platform and also supports different cloud storage providers. I didn’t find anything about encryption though.