Salamandar [1] filed a request to merge syncthing-gtk [2] into syncthing-gtk-python3 [3]:
Upstream is dead, maintainer dropped the package. At least the other package is based on a fork that has merged python3 support. [1] https://aur.archlinux.org/account/Salamandar/ [2] https://aur.archlinux.org/pkgbase/syncthing-gtk/ [3] https://aur.archlinux.org/pkgbase/syncthing-gtk-python3/
