I’ve tested windows and core and they are completely the same (exept core is portable and has smaller size). Is there any reason to use windows or gtk version over core?
These aren’t different versions, they are all wrappers on top of Syncthing core (except core obviously). It’s mostly about integration into the system, to make the UI “feel native”. The core web UI is just that, a web UI. If you don’t care about status icons and so on, you are likely fine with just core (wrappers do have more features, e.g. Synctrayzors conflict resolution tool).